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