#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define int ll
#define rep(i,a,b) for(int i = a; i < (b); i++)
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()
#define PB push_back
#define FS first
#define SD second
#define cmx(x,y) x = max(x,y)
#define cmn(x,y) x = min(x,y)
#define ary(k) array<int,k>
typedef pair<int,int> pii;
typedef vector<int> vi;

const int g = 10;

long double geth(long double v, long double tan, long double x) {
    long double vx = sqrtl((long double)(v*v) / (1 + tan*tan));
    long double vy = sqrtl(v*v-vx*vx);
    long double t = x / vx;
    long double h = vy * t - g * t*t/2;
    return h;
}

long double ternary(int x, int v) {
    long double pocz = 0, kon = 1e9;
    while (kon - pocz > 1e-4) {
        long double tan1 = (2*pocz + kon) / 3, tan2 = (pocz+2*kon)/3;
        long double h1 = geth(v, tan1, x), h2 = geth(v, tan2, x);
        if (h1 > h2) {
            kon = tan2;
        } else {
            pocz = tan1;
        }
    }
    return (pocz + kon) / 2;
}

long double bs(int x, int y, int v, bool left, long double peakx) {
    long double pocz = 0, kon = 1e9;
    if (left)
        kon = peakx;
    else
        pocz = peakx;
    while (kon - pocz > 1e-4) {
        long double tan = (pocz + kon) / 2;
        long double vx = sqrtl((long double)(v*v) / (1 + tan*tan));
        long double vy = sqrtl(v*v-vx*vx);
        long double t = x / vx;
        long double h = vy * t - g * t*t/2;
//        cerr << tan << " " << vx << " " << t << " " << h << "\n";
        bool collide = (h <= y + 1e-6);
        if (collide && left)
            pocz = tan;
        else if (collide)
            kon = tan;
        else if (left)
            kon = tan;
        else
            pocz = tan;
    }
    return (pocz + kon) / 2;
}

void fun() {
    int c, n;
    cin >> c >> n;
    long double low = 0, high = 1e9;
    for (int i = 0; i < n; i++) {
        int x, y;
        cin >> x >> y;
        long double mid = ternary(x, c);
//        cerr << mid << " " << bs(x, y, c, true, mid) << " " << bs(x, y, c, false, mid) << "\n";
        low = max(low, bs(x, y, c, true, mid));
        high = min(high, bs(x, y, c, false, mid));
    }
    cout << fixed << setprecision(3) << (low+high)/2 << "\n";
}

signed main(){
	cin.tie(0)->sync_with_stdio(0); cin.exceptions(cin.failbit);
    int z;
    cin >> z;
    while (z--) fun();
}