#include <stdio.h>
int main() {
    int t, i;
    scanf("%d", &t);
    float a[t];
    for (i = 0; i < t; i++) {
        a[i] = 0;
    }
    i = 0;
    while (t > i) {
        int n, m;
        scanf("%d %d", &n, &m);
        n = n - 1;
        if (m % n == 0) {
            a[i] = 0;
        } else {
            int x;
            float c;
            float b;
            x = (m / n) + 1;
            c = m - x * (n - 1);
            b = (float)m / (float)n;
            c = b - c;
            a[i] = c;
        }
        i++;
    }
    for (i = 0; i < t; i++) {
        if (a[i] == 0) {
            printf("CSFNB!\n");
        } else {
            printf("%f\n", a[i]);
        }
    }
}