#include <bits/stdc++.h>
#define ff first
#define ss second
using namespace std;

typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

int main() {
    cin.tie(0); ios_base::sync_with_stdio(0);
    int T; cin >> T;
    while (T--) {
        int C; cin >> C;
        int n; cin >> n;
        vector<pair<int, int>> a(n);
        for (auto &[x, y] : a) cin >> x >> y;
        
        int x_max = 0;
        for (auto [x, y] : a) x_max = max(x_max, x);

        long double l = 0, r = 1e18;
        for (auto [x, y] : a) {
            long double A = 5.0 * x * x / C / C;

            long double sq = sqrt((long long)x * x - 4 * A * (A + y));
            l = max(l, (x - sq) / (2 * A));
            r = min(r, (x + sq) / (2 * A));
        }
        long double A = 5.0 * x_max / C / C;
        l = max(l, (1 - sqrt(1 - 4 * A * A)) / (2 * A));
        r = min(r, (1 + sqrt(1 - 4 * A * A)) / (2 * A));

        cout.precision(3);
        cout << fixed << (l + r) / 2 << '\n';
    }
}