#include <bits/stdc++.h>
#define fi first
#define se second
#define mk make_pair
#define pii pair<int, int>
#define pll pair<ll, ll>
#define VT vector
#define pb push_back
#define SZ(a) ((int)a.size())
#define all(a) a.begin(), a.end()
#define TP template <class o>
#define TPP template <typename t1, typename t2>
#define rep(i, a, b) for (int i = a, i##ed_ = b; i <= i##ed_; i++)
#define REP(i, a, b) for (int i = b, i##st_ = a; i >= i##st_; i--)
#define FOR(i, n) rep(i, 1, n)
#define debug(x) cerr << #x << ' ' << '=' << ' ' << x << endl
using namespace std;
typedef double db;
typedef unsigned ui;
typedef long long ll;
typedef __int128 lll;
typedef long double ld;
typedef unsigned long long ull;

// char buf[1 << 20],*p1=buf,*p2=buf;
#define gc getchar() //(p1==p2&&(p2=(p1=buf)+fread(buf,1,1<<20,stdin),p1==p2)?EOF:*p1++)
TP void qr(o& x) {
    char c = gc; x = 0; int f = 1; 
    while (!isdigit(c)) {if (c == '-') f = -1; c = gc;}
    while (isdigit(c)) x = x * 10 + c - '0', c = gc;
    x *= f;
}
template <class o, class... O> void qr(o& x, O&... y) { qr(x), qr(y...); }
TP void qw(o x) {
    if (x < 0) putchar('-'), x = -x;
    if (x / 10) qw(x / 10);     
    putchar(x % 10 + '0');
}
TP void pr1(o x) { qw(x), putchar(' '); }
template <class o, class... O> void pr1(o x, O... y) { pr1(x), pr1(y...); }
TP void pr2(o x) { qw(x), putchar(10); }
template <class o, class... O> void pr2(o x, O... y) { pr2(x), pr2(y...); }
TP bool cmax(o& x, o y) { return (x < y ? x = y, 1 : 0); }
TP bool cmin(o& x, o y) { return (x > y ? x = y, 1 : 0); }
void yes(bool v) {puts(v ? "yes" : "no");}
void YES(bool v) {puts(v ? "YES" : "NO");}
void Yes(bool v) {puts(v ? "Yes" : "No");}
TP void order(VT<o> &a) { sort(all(a)); a.resize(unique(all(a)) - a.begin());}
TP int get_id(VT<o> &a, const o& val) {return lower_bound(all(a), val) - a.begin();}
TP void sort(o &v) {sort(all(v));}
TP o sorted(o v) {return sort(v), v;}
TP void reverse(o &v) {reverse(all(v));}
TP o reversed(o v) {return reverse(v), v;}
TP void unique(VT<o> &v) {v.erase(unique(all(v)), v.end());}
TP VT<o> uniqued(VT<o> v) {return unique(v), v;}
ll power(ll a, ll b, ll mod) {ll c=1; for(;b;b/=2,a=a*a%mod) if(b&1)c=c*a%mod;return c;}
TP o Pow(o a, ll b) {o c=o(1); for(; b;b/=2,a=a*a) if(b&1) c=c*a; return c;}

namespace geo {//Geometry几何
    typedef double db;
    typedef long double ld;
    const int N = 210, M = 2e4 + 10;
    const db eps = 1e-13, inf = 1.0 / 0.0, PI = acosl(-1.0); //精度
    int sign(db x) {return x < -eps ? -1: (x > eps ? 1: 0);} // 符号位
    
    struct P { // Point
        db x, y;
        P(db x = 0, db y = 0):x(x),y(y){}
        TPP P(pair<t1, t2> a): x(a.fi), y(a.se) {}
        P operator +(P b) const {return P(x + b.x, y + b.y);}
        P operator -(P b) const {return P(x - b.x, y - b.y);}
        P operator *(db t) const {return P(x * t, y * t);} // 数乘
        P operator /(db t) const {return P(x / t, y / t);} 
        friend db dot(P a, P b) {return a.x * b.x + a.y * b.y;}//点乘
        db operator *(P b) const {return x * b.y - y * b.x;} // 叉积
        db operator ^(P b) const {return x * b.x + y * b.y;} // 点乘
        db len() {return hypotl(x, y);} //求模长
        friend db dis(P a, P b) {return (a - b).len();} // 两点距离
        friend P normal(P a) {return P(-a.y, a.x);} //法向量(逆时针旋转90度)
        friend P unit(P a) {return a / a.len();} //单位化
        friend db slope(P a, P b) {return (b.y - a.y) / (b.x - a.x);} // 斜率
        friend db angle(P a, P b) {return atan2(b.y - a.y, b.x - a.x); } // b -> a 的极角
        friend db area(P a, P b, P c) {return fabs((c - a) * (b - a)) / 2;} // 三角形面积
        
        bool operator <(const P &b) const {return sign(x - b.x) ? x < b.x: y < b.y;}
        bool operator ==(const P &b) const {return sign(x - b.x) == 0 && sign(y - b.y) == 0;}
        
        P turn(db t) { //顺时针旋转 t(theta)(弧度)
            return P(x * cos(-t) + y * sin(t), x * sin(-t) + y * cos(t));
        }
        P Turn(P b, db t) {// 绕b点顺时针旋转 t(theta)(弧度)
            P c = *this - b;
            return c.turn(t) + b;
        }
        
        void in() {scanf("%lf %lf", &x, &y);}
        void out() {printf("%.5lf %.5lf\n", x, y);} // 注意输出位数
    } q[N]; // 注意q是用来存凸包的
    
    int judge(P a, P b, P c) {return sign((b - a) * (c - a)) > 0;} // a,b,c严格逆时针(有序)
    int L_have(P s, P t, P p) {return !sign((p - s) * (t - s));}//直线上有点p
    int S_have(P s, P t, P p) {return !sign((p - s) * (t - s)) && sign(dot(p - s, p - t)) <= 0;} //线段上有点p
    
    int PICP(P *a, int n, P p) { // Point In Convex Polygon. p是否在凸多边形a外 (0: 内. 1: 边界, 2: 外)
        if(judge(a[1], p, a[2]) || judge(a[n], p, a[1])) return 2;
        if(S_have(a[1], a[2], p) || S_have(a[1], a[n], p)) return 1;
        int l = 2, r = n - 1, mid;
        while(l < r) { // 以 a[1] 为极点, 看p的极角在哪条边中间
            mid = (l + r + 1) >> 1;
            if(judge(a[1], a[mid], p)) l = mid;
            else r = mid - 1;
        }
        if(judge(a[l], p, a[l + 1])) return 2;
        return S_have(a[l], a[l + 1], p);
    }
    
    int PIP(int *a, int n, P p) { // Point in Polygon. (点的顺序是逆/顺时针给出) (return 0: 内. 1: 边界, 2: 外)
        // 回转数算法.
        a[n + 1] = a[1];
        FOR(i, n) if(S_have(a[i], a[i + 1], p)) return 1;
        db sum = 0, l = angle(p, a[1]), r, d;
        FOR(i, n) {
            r = angle(p, a[i + 1]);
            d = r - l;
            if(d >= PI) d -= 2 * PI;
            else if(d < -PI) d += 2 * PI;
            sum += d;
        }
        // 内部 sum = 2PI, 外部 sum = 0. 这里简单以PI为分界线
        return abs(sum) < PI ? 2: 0;
    }
    
    // #define Half // 半平面交时要求斜率的弧度
    struct L { //Line: 线段(segment/ S), 射线(ray/ R), 直线(line/ L)
        P s, t; 
        L(P s, P t):s(s), t(t){init();}
        L(){}
        void in() {s.in(); t.in(); init();}
        
        #ifdef Half 
            ld k; // 只有半平面交时需要的极角
        #endif
        void init() {
            #ifdef Half
                k = angle(s, t);
            #endif
        }
        #ifdef Half
            bool operator <(L b) const {
                return sign(b.k - k) ? k < b.k: b.judge(s);
            }
        #endif
        
        db len() {return (t - s).len();} // 线段长度
        int judge(P b) {return geo::judge(s, t, b);}// 是否在半开平面内(向量左侧)
        db crossRatio(L b) {
            if(sign((t - s) * (b.t - b.s)) == 0) return inf;
            return ((b.s - s) * (b.t - b.s))  /  ((t - s) * (b.t - b.s));
        }
        P R2P(db r) {return s + (t - s) * r;} // Ratio to Point
        VT<P> operator &(L b) { //直线交点
            db r = crossRatio(b);
            if(r == inf) return {};
            return {R2P(r)};
        }
        // * 平行或共线不算交
        bool S_cross(L b, bool s = 0) { //线段是否有交. s:strict. s=1时, 交点不能是端点.
            db x = crossRatio(b), y = b.crossRatio(*this);
            return sign(x) >= s && sign(1 - x) >= s && 
                   sign(y) >= s && sign(1 - y) >= s;
        }
        db P2S(P p) { // 点p到线段的距离
            if(s == t) return (s - p).len();
            P x = p - s, y = p - t, z = t - s;
            if(sign(dot(x, z)) < 0) return x.len();
            if(sign(dot(y, z)) > 0) return y.len();
            return fabs((x * z) / z.len()); // 点到直线距离
        }
        db P2L(P p) {// 点到直线距离
            return 2 * area(s, t, p) / dis(s, t); 
        }
        P Foot_point(P p) { //点到直线的垂足
            P x = p - s, y = p - t, z = t - s;
            db u = dot(x, z), v = -dot(y, z); //求投影
            return s + z * (u / (u + v));
        }
        P Sym_point(P p) {//symmetry point 对称点
            return Foot_point(p) * 2 - p;
        }
    };
    
    struct Cir: P { // 圆
        db r;
        Cir(db x = 0, db y = 0, db r = 0):P(x, y), r(r){}
        void out() {printf("%.1lf %.1lf %.5lf\n", x, y, r);} 
        db P2C(P b) { // Point to Circle
            return max((db)0, dis(P(*this), b) - r);
        }
        P rotate(db theta) { // 圆上theta弧度对应位置
            return P(x + cos(theta) * r, y + sin(theta) * r);
        }
        friend vector<L> out_tangent(Cir A, Cir B) { // 外公切线
            db d = dis(A, B);
            if(d <= abs(A.r - B.r)) return {}; // 内含
            VT<L> res;
            db theta = angle(A, B) + PI / 2, ang = asin((B.r - A.r) / d);
            res.emplace_back(A.rotate(theta + ang), B.rotate(theta + ang)); // 左侧指向圆外
            res.emplace_back(B.rotate(theta - ang - PI), A.rotate(theta - ang - PI));
            return res;
        }
        friend vector<L> in_tangent(Cir A, Cir B) {
            db d = dis(A, B);
            if(!sign(d - A.r - B.r)) { // 外切
                P p = A + (B - A) * (A.r / d);
                return {L(p, p + normal(B - A))};
            }
            if(d < A.r + B.r) return {};
            VT<L> res;
            db theta = angle(A, B), ang = acos((B.r + A.r) / d);
            res.emplace_back(A.rotate(theta - ang), B.rotate(theta - ang + PI));
            res.emplace_back(A.rotate(theta + ang), B.rotate(theta + ang + PI));
            return res;
        }
    };
    
    int Convex_hull(P *a, int n, P *q) { // 输入a[1...n]. 返回凸包点数, 凸包顶点存到q(逆时针)
        assert(n >= 0);
        if(n <= 2) {
            FOR(i, n) q[i] = a[i];
            q[n + 1] = q[1];
            return n;
        }
        sort(a + 1, a + n + 1);
        int r = 0;
        FOR(i, n) {//下凸壳
            while(r > 1 && !judge(q[r - 1], q[r], a[i])) r--;
            q[++r] = a[i];
        }
        int st = r;
        REP(i, 1, n - 1) {//上凸壳
            while(r > st && !judge(q[r - 1], q[r], a[i])) r--;
            q[++r] = a[i];
        }
        return --r; // a[1]会存两遍, 所以要-1
    }
    
    db Max_dis(P *a, int n) { //旋转卡壳求最远点对
        if(n < 2) return 0;
        int m = Convex_hull(a, n, q);
        db ans = dis(q[1], q[2]);
        for(int i = 1, j = 2; i <= m; i++) {
            P &x = q[i], &y = q[i + 1];
            while(area(x, y, q[j]) < area(x, y, q[j + 1])) j = j % m + 1;
            cmax(ans, (x - q[j]).len());
            cmax(ans, (y - q[j]).len());
        }
        return ans;
    }
    
    bool cmp_x(P x, P y) {return x.x < y.x;}
    bool cmp_y(P x, P y) {return x.y < y.y;}
    db min_dis; void upd(const P &u, const P &v) {cmin(min_dis, dis(u, v)); }
    void get_min(P *p, int l, int r) { // [l, r]
        if(r - l <= 4) {
            rep(i, l, r) rep(j, i + 1, r) 
                upd(p[i], p[j]);
            return sort(p + l, p + r + 1, cmp_y);
        }
        int mid = (l + r) >> 1;
        db midx = p[mid].x;
        get_min(p, l, mid); 
        get_min(p, mid + 1, r);
        inplace_merge(p + l, p + mid + 1, p + r + 1, cmp_y); 
        static P t[N]; 
        int m = 0;
        rep(i, l, r) {
            auto now = p[i];
            db dx = abs(now.x - midx);
            if(dx < min_dis) {
                for(int j = m; j > 0 && (now.y - t[j].y) <= min_dis; j--)
                    upd(now, t[j]);
                t[++m] = now;
            }
        }
    }
    db Min_dis(P *a, int n) { // 最近点对距离
        sort(a + 1, a + n + 1, cmp_x); // * Note: 会改变a数组
        min_dis = inf; get_min(a, 1, n);
        return min_dis;
    }
    
    db Min_matrix(P *a, int n) {//最小矩形覆盖
        if(n <= 2) return 0;
        int m = Convex_hull(a, n, q);
        db ans = inf; P A, B, C, D;
        int j = 2, l = 2, r = 2;
        FOR(i, m) {
            P v = q[i + 1] - q[i], S = q[i]; // 确定矩形一边所在直线
            while(v * (q[j] - S) < v * (q[j + 1] - S)) j = j % m + 1; // 确定高度
            while(dot(v, q[r + 1] - S) > dot(v, (q[r] - S))) r = r % m + 1;
            if(i == 1) l = r;
            while(dot(v, q[l + 1] - S) < dot(v, (q[l] - S))) l = l % m + 1;
            if(cmin(ans, dot(v, q[r] - q[l]) * fabs((q[j] - S) * v) / dot(v, v))) {
                v = v / v.len(); //单位化
                P u = normal(v); //法向量
                // A,B,C,D逆时针排列
                A = v * dot(v, q[l] - S) + S;
                B = v * dot(v, q[r] - S) + S;
                db h = v * (q[j] - S);
                C = B + u * h;
                D = A + u * h;
            }
        }
        printf("%.5lf\n", ans);
        A.out(); B.out(); C.out(); D.out(); //四个顶点
        return ans;
    }
    
    #ifdef Half
    int Half_plane(L *a, int n, P *p) { //半平面交, 需要在前面 #define Half. 
        // a[1...n] 表示半平面, p为凸包上的点, 返回点数
        sort(a + 1, a + n + 1);
        int l = 1, r = 1;
        rep(i, 2, n) if(a[i].k - a[r].k > eps) {
            while(l < r && !a[i].judge(a[r - 1] & a[r])) r--;
            while(l < r && !a[i].judge(a[l] & a[l + 1])) l++;
            a[++r] = a[i];
            //注意:这里的实现把a数组覆盖了, 如果不想修改a,要开个新的数组
        }
        while(l < r && !a[l].judge(a[r] & a[r - 1])) r--; // r已经删掉不需要的l了,现在l删r
        n = 0;
        if(r - l > 1) { // 如果有无解的情况,那么一开始要加上无穷大的边界(四个), 最后r - l <= 1 就是无解.
            a[r + 1] = a[l]; 
            rep(i, l, r) p[++n] = a[i] & a[i + 1];
        }
        return n;
    }
    #endif
    
    int Mincowski(P *a, int n, P *b, int m, P *c) {//闵可夫斯基合并凸包(x∈A,y∈B,x+y∈C)
        static P v1[N], v2[N]; 
        int t = 1; c[t] = a[1] + b[1];
        a[n + 1] = a[1]; b[m + 1] = b[1];
        FOR(i, n) v1[i] = a[i + 1] - a[i];
        FOR(i, m) v2[i] = b[i + 1] - b[i];
        int i = 1, j = 1;
        while(i <= n && j <= m) ++t, c[t] = c[t - 1] + (v1[i] * v2[j] > 0 ? v1[i++]: v2[j++]);
        while(i <= n) ++t, c[t] = c[t - 1] + v1[i++];
        while(j <= m) ++t, c[t] = c[t - 1] + v2[j++];
        return t;
    }
    
    db Area(P *a, int n) { //求面积
        db s = 0; a[n + 1] = a[1];
        FOR(i, n) s += a[i] * a[i + 1];
        return abs(s) / 2;
    }

    int n, m;
    db vy, ans = inf;
    L seg[N];
    pii a[N]; P p[N];
    db f[N];
    
    bool check(L s, int u, int v) {
        FOR(i, n) 
            if(i != u && i != v && s.S_cross(seg[i], 0)) 
                return 0;
        return 1;
    }
    
    bool valid[N];
    
    void solve() {
        qr(n, m, vy);
        FOR(i, 2 * n) {
            qr(a[i].fi, a[i].se);
            p[i] = P(a[i]);
            int x = a[i].fi, y = a[i].se;
            if(i % 2 == 0) {
                seg[i / 2] = L(p[i - 1], p[i]);
                if(abs(a[i - 1].fi - a[i].fi) == 2 * m) {
                    return pr2(-1);
                }
            }
        }
        fill(f + 1, f + 2 * n + 1, inf);
        using T = pair<db, int>;
        priority_queue<T, VT<T>, greater<T>> q;
        
        P s(0, -1e9), t(0, 1e9); // ! 源汇点
        a[0] = {0, -1e5}; p[0] = P(a[0]);
        f[0] = 0; q.push({0, 0}); valid[0] = 1;
        
        FOR(i, 2 * n) {
            valid[i] = a[i].fi != -m && a[i].fi != m;
            if(valid[i] && check(L(s, p[i]), (i + 1) / 2, 0)) {
                f[i] = 0;
                q.push({0, i});
            }
        }
        
        while(q.size()) {
            auto [dis, x] = q.top(); q.pop();
            if(sign(dis - f[x])) continue; 
            // debug(x); debug(dis);
            if(check(L(p[x], t), (x + 1) / 2, 0)) {
                // debug("end");
                // debug(x);
                cmin(ans, f[x]);
                continue;
            }
            FOR(y, 2 * n) {
                if(a[x].se >= a[y].se || !valid[y]) continue;
                L seg(p[x], p[y]);
                if(check(seg, (x + 1) / 2, (y + 1) / 2) && cmin(f[y], max(f[x], vy / fabs(slope(p[x], p[y]))))) {
                    // debug(slope(p[x], p[y]));
                    q.push({f[y], y});
                }
            }
        }
        
        if(ans == inf) pr2(-1);
        else printf("%.15lf\n", ans);
    }
}

int main() {
    int T = 1;
    // qr(T);
    FOR(t, T) {
        geo::solve();
    } 
    return 0;
}