#include <iostream>
#include <cstdio>
using namespace std;
int main() {
    int InputTime;
    cin >> InputTime;
    while (InputTime--) {
        float NumPeople, NumMoney;
        cin >> NumPeople >> NumMoney;
        float ShouldEachPeopleMoney = NumMoney / (NumPeople - 1.0);
        int RealyEachPay;
        if ((int(NumMoney) % int(NumPeople - 1)) == 0) {
            RealyEachPay = NumMoney / (NumPeople - 1);
        } else {
            RealyEachPay = NumMoney / (NumPeople - 1) + 1;
        }
        float tt = RealyEachPay * 1.0;
        float Interest;
        Interest = (tt - ShouldEachPeopleMoney) * (NumPeople - 2.0) * 1.0;
        if (Interest > 0) {
            printf("%.6f\n", Interest);
        } else {
            printf("CSFNB!\n");
        }
    }

    return 0;
}