#include <iostream>
#include <cstdio>
#include <cmath>
#include <algorithm>

using namespace std;
typedef long long ll;

int main() {
    // freopen("test.txt", "r", stdin);
    int T;
    int n, m;
    scanf("%d", &T);
    while (T--) {
        scanf("%d %d", &n, &m);
        if (m % (n - 1) == 0) {
            printf("CSFNB!\n");
        } else {
            double part = 1.0 * m / (n - 1);
            double res = ((n - 2) * ceil(part) + part) - m;
            printf("%.6f\n", res);
        }
    }
    return 0;
}