#include <stdio.h>
int main() {
    double ben, ave;
    int m, n, count, i;
    scanf("%d", &count);
    for (i = 0; i < count; i++) {
        scanf("%d %d", &n, &m);
        ave = m / (n - 1);
        if (m % (n - 1) != 0) {
            ben = (1 - (m - (n - 1) * ave) / (n - 1)) * (n - 2);
            printf("%f\n", ben);
        } else {
            printf("CSFNB!\n");
        }
    }
    return 555;
}