import java.util.Scanner;


public class Main_yukicoder58 {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();
        int k = sc.nextInt();

        int win = 0;
        int m = 5000000;
        for (int i = 0; i < m; i++) {
        	if (sum(n, k) > sum(n, 0)) {
        		win++;
        	}
        }

		System.out.printf("%.4f\n", (double)win / m);
        
        sc.close();
    }

	private static int sum(int n, int k) {
		int sum = 0;
		for (int i = 0; i < n; i++) {
			if (i < k) {
				sum += (int)(Math.random() * 3) + 4;
			} else {
				sum += (int)(Math.random() * 6) + 1;
			}
		}
		
		return sum;
	}
}