#include <iostream>
#include <cmath>
using namespace std;

typedef long long LL;
const int INF = 0x3f3f3f3f;
const LL LINF = 0x3f3f3f3f3f3f3f3f;

int main() {
    int N;
    scanf("%d", &N);
    while (N--) {
        int n, m;
        scanf("%d%d", &n, &m);
        n--;
        if (n <= 1 || !(m % n)) {
            printf("CSFNB!\n");
            continue;
        }
        double avr = 1.0 * m / n;
        int upp = ceil(avr);
        double ans = (n - 1) * (upp - avr);
        printf("%lf\n", ans);
    }
    return 0;
}