#include <bits/stdc++.h>
using namespace std;
int main() {
    std::ios::sync_with_stdio(false);
    int T;
    cin >> T;
    while (T--) {
        int n, m;
        cin >> n >> m;
        double ans = 0;
        ans = m * 1.0 / (n - 1);
        ans = (ceil(ans) - ans) * (n - 2);
        if (ans > 0)
            printf("%.6f", ans);
        else
            cout << "CSFNB";
        cout << endl;
    }
    return 0;
}