#include <iostream>
#include <cmath>

using namespace std;

int main() {
    int T;
    scanf("%d", &T);
    while (T--) {
        double n, m;
        scanf("%lf%lf", &n, &m);
        n -= 1.0;

        double delta = (ceil(m / n) * n - m) * (n - 1) / n;
        if (delta > 5e-7) {
            printf("%.6lf\n", delta);
        } else {
            printf("CSFNB!\n");
        }
    }
}