#include <bits/stdc++.h>

using namespace std;

const int maxc = 1000025;

const int g = 10;

using llf = long double;
const llf PI = acos(-1);

pair<llf,llf> SO(llf C, llf X, llf Y) {
    const auto f = [&](llf TAN) {
        // llf t = X / vx;
        // llf vy = sqrt(max<llf>(0, C*C-vx*vx));
        // return t * vy - 0.5 * g * t * t;
        const llf SEC2 = TAN*TAN+1;
        return X * TAN - 0.5 * g * X * X * SEC2 / C / C;
    };

    llf l = 0, r = 1e9;
    for (int iter = 0; iter < 100; iter++) {
        llf m1 = (l * 2 + r) / 3;
        llf m2 = (l + r * 2) / 3;
        if (f(m1) < f(m2)) {
            l = m1;
        } else {
            r = m2;
        }
    }
    llf mx = (l+r)/2;
    l = 0, r = mx;
    for (int iter = 0; iter < 100; iter++) {
        llf m = (l + r) / 2;
        if (f(m) <= Y) {
            l = m;
        } else {
            r = m;
        }
    }
    llf L = (l+r)/2;
    l = mx, r = 1e9;
    for (int iter = 0; iter < 100; iter++) {
        llf m = (l + r) / 2;
        if (f(m) <= Y) {
            r = m;
        } else {
            l = m;
        }
    }
    llf R = (l+r)/2;
    // cerr << "Y = " << Y << endl;
    // cerr << f((0+L)/2) << ' ';
    // cerr << f(L) << ' ' << f((L+R)/2) << ' ';
    // cerr << f(R) << ' ';
    // cerr << f((R+C)/2) << ' ' << f(C) << ' ';
    // cerr << endl;
    return { L, R };
}

signed main() {
    cin.tie(nullptr) -> sync_with_stdio(false);
    int T;
    cin >> T;
    while (T--) {
        int C;
        cin >> C;
        int N;
        cin >> N;
        vector<pair<llf,int>> seg;
        llf mx = -1e9;
        llf mn = 1e9;
        for (int i = 0; i < N; i++) {
            int x, y;
            cin >> x >> y;
            auto [l, r] = SO(C, x, y);
            mx = max(mx, l);
            mn = min(mn, r);
            // seg.emplace_back(l, -1);
            // seg.emplace_back(r, 1);
            // cerr << l << ',' << r << endl;
        }
        // const auto gettan = [&C](llf vx) {
        //     llf vy = sqrt(max<llf>(0, C*C-vx*vx));
        //     return vy / vx;
        // };
        assert (mx <= mn);
        cout << fixed << setprecision(3);
        cout << (mx+mn)/2 << '\n';
        // sort(seg.begin(), seg.end());
    }
}