#include <iostream>
#include <iomanip>
using namespace std;
int main() {
    int n;
    cin >> n;
    int *a = new int[n];
    int *b = new int[n];
    for (int i = 0; i < n; i++) {
        cin >> a[i] >> b[i];
    }
    for (int i = 0; i < n; i++) {
        if (b[i] % (a[i] - 1) == 0) {
            cout << "CSFNB!" << endl;
        } else {
            int u;
            u = b[i] / (a[i] - 1) + 1;
            double k;
            k = (double)(u * (a[i] - 1) - b[i]) / (a[i] - 1) * (a[i] - 2);
            cout << setiosflags(ios::fixed);
            cout << setprecision(6) << k << endl;
        }
    }
    delete[] a;
    delete[] b;
    return 0;
}