import java.util.Scanner;

public class OJ_1007 {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        double[] ans = new double[n];
        for (int i = 0; i < n; i++) {
            int person = in.nextInt() - 1;
            int cost = in.nextInt();
            if (cost % person == 0) {
                ans[i] = 0;
            } else {
                ans[i] = (cost / person + 1) * (person - 1) + (double) cost / person - cost;
                ans[i] = (cost / person + 1 - (double) cost / person) * (person - 1);
            }
        }
        for (int i = 0; i < n; i++) {
            if (ans[i] == 0) {
                System.out.println("CSFNB!");
            } else {
                System.out.printf("%.6f%n", ans[i]);
            }
        }
        in.close();
    }
}