#include <iostream>
#include <cmath>

using namespace std;

int main() {
    int T;
    scanf("%d", &T);
    while (T--) {
        double n, m;
        scanf("%lf%lf", &n, &m);
        n -= 1.0;

        double delta = (ceil(m / n) * n - m) * (n - 1) / n;
        if (delta > 5e-7) {
            printf("%.6lf\n", delta);
        } else {
            printf("CSFNB!\n");
        }
    }
}

/sandbox/1/a.cpp: In function 'int main()':
/sandbox/1/a.cpp:8:5: error: 'scanf' was not declared in this scope
     scanf("%d", &T);
     ^~~~~
/sandbox/1/a.cpp:8:5: note: suggested alternative: 'wscanf'
     scanf("%d", &T);
     ^~~~~
     wscanf
/sandbox/1/a.cpp:16:13: error: 'printf' was not declared in this scope
             printf("%.6lf\n", delta);
             ^~~~~~
/sandbox/1/a.cpp:16:13: note: 'printf' is defined in header '<cstdio>'; did you forget to '#include <cstdio>'?
/sandbox/1/a.cpp:3:1:
+#include <cstdio>
 
/sandbox/1/a.cpp:16:13:
             printf("%.6lf\n", delta);
             ^~~~~~
/sandbox/1/a.cpp:18:13: error: 'printf' was not declared in this scope
             printf("CSFNB!\n");
             ^~~~~~
/sandbox/1/a.cpp:18:13: note: 'printf' is defined in header '<cstdio>'; did you forget to '#include <cstdio>'?