#include <bits/stdc++.h>

using namespace std;

int main() {
    int c;
    scanf("%d", &c);
    while (c--) {
        int n;
        double m;
        scanf("%d", &n);
        scanf("%lf", &m);
        double x = ceil(m / (n - 1)) - m / (n - 1);
        if (x == 0) {
            printf("CSFNB!\n");
        } else {
            printf("%.6lf\n", n, x * (n - 2));
        }
    }
    return 0;
}