#include <iostream>

double csf(int m, int n) {
    double g;
    int c = m / (n - 1) + 1;
    c *= (n - 2);
    g = (double)m / (n - 1);
    g = g + c - m;
    return g;
}
int main() {
    int T;
    scanf("%d", &T);
    for (int i = 0; i < T; i++) {
        int n, m;
        scanf("%d %d", &n, &m);
        if (csf(m, n) <= 0)
            printf("CSFNB!\n");
        else
            printf("%.6lf\n", csf(m, n));
    }
    return 0;
}