import java.util.*;

public class Main {
	public static void main (String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int k = sc.nextInt();
		double[] rateA = new double[n * 6 + 1];
		double[] rateB = new double[n * 6 + 1];
		rateA[0] = 1;
		rateB[0] = 1;
		for (int i = 0; i < n; i++) {
		    double[] nextA = new double[n * 6 + 1];
		    double[] nextB = new double[n * 6 + 1];
		    for (int j = i; j < i * 6 + 1; j++) {
		        for (int a = 1; a <= 6; a++) {
		            nextA[j + a] += rateA[j] / 6;
		            if (i < k && a <= 3) {
		                nextB[j + a + 3] += rateB[j] / 6;
		            } else {
		                nextB[j + a] += rateB[j] / 6;
		            }
		        }
		    }
		    rateA = nextA;
		    rateB = nextB;
		}
		double rate = 0;
		for (int i = 1; i <= n * 6; i++) {
		    rateA[i] += rateA[i - 1];
		    rate += rateB[i] * rateA[i - 1];
		}
		System.out.println(rate);
   }
}