#include <bits/stdc++.h>
#define ll long long

using namespace std;

ll n, m;
int main() {
    cin >> n >> m;
    if (m % (n - 1))
        printf("CSFNB!");
    else {
        int ave = (n + m - 1) / (n - 1);
        double ave2 = (double)m / (n - 1);
        double ans = ave2 + ave * (n - 2) - m;
        printf("%.6lf", ans);
    }
}