#include <iostream>
#include <cstdio>
#include <cmath>
using namespace std;
int main() {
    int n, num[20], batch;
    double s[20], bonus;

    cin >> n;

    for (int i = 0; i < n; i++) {
        cin >> num[i] >> s[i];
    }

    for (int i = 0; i < n; i++) {
        batch = ceil(s[i] / (num[i] - 1));
        if (batch == (s[i] / (num[i] - 1)))
            cout << "CSFNB!" << endl;
        else {
            bonus = (num[i] - 2) * (batch - (s[i] / (num[i] - 1)));
            printf("%.6f\n", bonus);
        }
    }

    return 0;
}