import java.util.Arrays;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int N = scan.nextInt();
		int K = scan.nextInt();
		scan.close();
		if(K == 0) {
			System.out.println(0.5);
			System.exit(0);
		}
		int a[] = new int[6 * N + 1];
		int b[] = new int[6 * N + 1];
		int [][]S = new int[N + 1][6 * N + 1];


		Arrays.fill(a, 0);
		Arrays.fill(b, 0);
		for(int i = 1; i <= 6; i++) {
			a[i] = 1;
			S[1][i] = 1;
		}
		for(int i = 2; i <= N; i++) {
			for(int j = i; j <= 6 * i; j++) {
				for(int k = 1; k <= 6; k++) {
					if(j - k <= 0) {
						break;
					}
					S[i][j] += S[i - 1][j - k];
				}
			}
		}


		int[][]S2 = new int[N + 1][6 * N + 1];
		for(int i = 1; i <= 6; i++) {
			if(i <= 3) {
				S2[1][i] = 0;
			}else {
				S2[1][i] = 1;
			}
		}
		for(int i = 2; i <= K; i++) {
			for(int j = i; j <= 6 * i; j++) {
				for(int k = 4; k <= 6; k++) {
					if(j - k <= 0) {
						break;
					}
					S2[i][j] += S2[i - 1][j - k];
				}
			}
		}
		if(N != K) {
			int n = N - K;
			for(int i = K + 1; i <= N; i++) {
				for(int j = i; j <= 6 * i; j++) {
					for(int k = 1; k <= 6; k++) {
						if(j - k <= 0) {
							break;
						}
						S2[i][j] += S2[i - 1][j - k];
					}
				}
			}
		}
		long d1 = 0;
		long d2 = 0;
		for(int i = N; i <= 6 * N; i++) {
			d1 += S[N][i];
			d2 += S2[N][i];
		}

		double ans = 0;
		for(int i = N; i <= 6 * N; i++) {
			for(int j = 0; j < i; j++) {
				ans += (double) (S2[N][i] * S[N][j]) / (d1 * d2);
			}

		}
		System.out.println(ans);

	}
}