#include <stdio.h>
void welfareValue(long int man, long int money) {
    long int avemoney = money / man;
    double realityavemoney = (double)money / man;
    if (avemoney < realityavemoney) {
        double totalmoney = (double)(avemoney + 1) * (man - 1) + realityavemoney;
        printf("%.6llf\n", totalmoney - money);
    } else
        printf("CSFNB!\n");
}
int main() {
    int n;
    scanf("%d", &n);
    long int man[n], money[n];
    for (int i = 0; i < n; i++) {
        scanf("%ld%ld", &man[i], &money[i]);
    }
    for (int i = 0; i < n; i++) {
        welfareValue(man[i] - 1, money[i]);
    }
}