#include <iostream>

double csf(int m, int n) {
    double g;
    if (m % (n - 1) == 0)
        return -1;
    else {
        n -= 1;
        int c = m / n + 1;
        g = c * (n - 1) - (m - m / n);
    }
    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("%.6f\n", csf(m, n));
    }
    return 0;
}