#include <stdio.h>
int main() {
    void func(int t);
    int m;
    func(m);
    return 0;
}
void func(int t) {
    int i = 0, a, b;
    scanf("%d", &t);
    int s[t][2];  //�Ҳ�̫�ᶨ�嶯̬���顣��������dev��û�б�����Ҳ���Ǻ������
    double c[t], s1[t][2];
    for (i = 0; i < t; i++) {
        scanf("%d %d", &s[i][0], &s[i][1]);
        if (s[i][1] % (s[i][0] - 1) == 0) {
            c[i] = 0;
        } else {
            a = s[i][1] % (s[i][0] - 1);
            b = (s[i][1] - a) / (s[i][0] - 1) + 1;
            a = s[i][1] - b * (s[i][0] - 2);
            s1[i][1] = s[i][1];
            s1[i][0] = s[i][0];
            c[i] = (s1[i][1]) / (s1[i][0] - 1) - a;
        }
    }
    for (i = 0; i < t; i++) {
        if (c[i] == 0) {
            printf("CSFNB!\n");
        } else {
            printf("%.6f\n", c[i]);
        }
    }
}