#include <stdio.h>
int main() {
    int a[20][2] = { 0 };
    int n;
    int i;
    double x;
    int y;
    scanf("%ld", &n);
    for (i = 0; i < n; i++) {
        scanf("%ld %ld", &a[i][0], &a[i][1]);
    }
    for (i = 0; i < n; i++) {
        if (a[i][1] % (a[i][0] - 1) == 0)
            y = a[i][1] / (a[i][0] - 1);
        else
            y = a[i][1] / (a[i][0] - 1) + 1;
        x = (y - ((double)a[i][1] / (double)(a[i][0] - 1))) * (a[i][0] - 2);
        if (x > 0) {
            printf("%.6lf\n", x);
        } else
            printf("CSFNB!");
    }
    return 0;
}