/*====Corycle====*/
#include <bits/stdc++.h>
#define ll long long
using namespace std;
const int inf = 0x3f3f3f3f;
const double eps = 1e-7;
int read() {
    int s = 0, f = 1;
    char c = getchar();
    while (c < '0' || c > '9') {
        if (c == '-')
            f = -1;
        c = getchar();
    }
    while (c >= '0' && c <= '9') {
        s = s * 10 + c - '0';
        c = getchar();
    }
    return s * f;
}
int n, m;
int main() {
    //	freopen("_.in","r",stdin);
    //	freopen("_.out","w",stdout);
    int T = read();
    while (T--) {
        n = read();
        m = read();
        double ans = ((m % (n - 1) ? m / (n - 1) + 1 : m / (n - 1)) - 1.0 * m / (n - 1)) * (n - 2);
        if (ans < eps)
            puts("CSFNB!");
        else
            printf("%.6lf\n", ans);
    }
    return 0;
}