#include <bits/stdc++.h> 

using namespace std;

typedef long long ll;
typedef long double ld;


const int N = (int)3e3 + 12, MOD = (int)1e9 + 7;


int n, s;

struct pt{
    int x, y;
};
void in(pt &a) {
    cin >> a.x >> a.y;
}
vector<array<pt, 2>> a;

ld dist(pt a, pt b) {
    ld x = (a.x - b.x) ,y = (b.y - a.y);
    return sqrtl(x * x + y * y);
}
bool check(pt x, pt y) {
    if(x.x == s) {
        if(y.x >= x.x) return 1;
    } else {
        if(y.x <= x.x) return 1;
    }
    if(x.y == s) {
        if(y.y >= x.y) return 1;
    } else {
        if(y.y <= x.y) return 1;
    }
    return 0;
}
ld get(pt x, pt y) {
    ld ret = (1e18);
    if(check(a[0][0], x) && check(a[0][1], y)) {
        ret = min(ret, dist(a[0][0], x) + dist(a[0][1], y) + s * 4);
        // cout << a[0][0].x << ' ' << a[0][0].y << ' ' << x.x << ' ' << x.y << '\n';
    }
    if(check(a[0][1], x) && check(a[0][0], y)) {
        ret = min(ret, dist(a[0][1], x) + dist(a[0][0], y) + s * 4);
    }
    return ret;
}
void test() {
    cin >> n >> s;
    a.resize(n);
    for(int i = 0; i < n; i++) {
        in(a[i][0]);in(a[i][1]);
    }
    ld res = s * 8;
    res = min({res, get({-s, -s}, {s, s}), get({-s, s}, {s, -s})});
    // cout << get({-s, s}, {s, -s}) << '\n';
    cout << fixed << setprecision(7) << res << '\n';
}

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);

    int t = 1;
    // cin >> t;

    while(t--) 
        test();

    return 0;
}