#include <iostream>
using namespace std;
int main() {
    int T;
    cin >> T;
    double a[T];
    double m[T];
    for (int i = 0; i < T; i++) {
        cin >> a[i];
        a[i] = a[i] - 1;
        cin >> m[i];
    }
    for (int i = 0; i < T; i++) {
        if (int(m[i]) % int(a[i]) == 0) {
            cout << "CSFNB!" << endl;
        } else {
            cout << fixed << (int(m[i]) / int(a[i]) + 1) * a[i] - m[i] / a[i] << endl;
        }
    }
    return 0;
}