#include <bits/stdc++.h>
using namespace std;
#define ulli unsigned long long int
#define F(i, n, m) for (int i = n; i <= m; i++)

inline int read() {
    bool w = 0;
    int s = 0;
    char ch = 0;
    while (!isdigit(ch)) w = ch == '-', ch = getchar();
    while (isdigit(ch)) s = (s << 3) + (s << 1) + (ch ^ 48), ch = getchar();
    return w ? -s : s;
}

inline void write(int x) {
    if (x < 0)
        putchar('-'), x = ~x + 1;
    if (x > 9)
        write(x / 10);
    putchar((x % 10) | 48);
}

int a[21], num[21];
bool iszs[100000001], uiszs[100000001];

bool zhishu(int g) {
    if (iszs[g] == 1)
        return true;
    if (uiszs[g] == 1)
        return false;
    bool p = 0;
    int t = int(sqrt(g));
    F(i, 2, t) {
        if (g % i == 0) {
            p = 1;
            break;
        }
    }
    if (p == 1) {
        uiszs[g] = 1;
        return false;
    } else {
        iszs[g] = 1;
        return true;
    }
}

bool nextnum(int n, int k) {
    bool end = 0;
    for (int i = k; i >= 1; i--) {
        if (num[i] == n - k + i)
            continue;
        num[i]++;
        F(j, i + 1, k)
        num[j] = num[i] + j - i;
        end = 1;
        break;
    }
    return end;
}

int main() {
    int n = read(), p, m;
    F(i, 1, n) {
        p = read();
        p--;
        m = read();
        if (m % p == 0) {
            printf("CSFNB!");
            continue;
        }
        printf("%.6f", (p - 1) * (m / p + 1 - double(m) / p));
    }

    return 0;
}