#include "bits/stdc++.h"
using namespace std;
#define MAX 100

double dp1[MAX];
double dp2[MAX];

int main(){
	int N, K;
	cin >> N >> K;
	dp1[0] = 1;
	dp2[0] = 1;
	for (int i = 0; i < N; i++)
	{
		for (int j = MAX - 10; j >= 0; j--)
		{
			for (int k = 1; k <= 6; k++)
			{
				dp1[j + k] += dp1[j] / 6;
			}
			dp1[j] = 0;
		}
	}


	for (int i = 0; i < K; i++)
	{
		for (int j = MAX - 10; j >= 0; j--)
		{
			for (int k = 4; k <= 6; k++)
			{
				dp2[j + k] += dp2[j] / 3;
			}
			dp2[j] = 0;
		}
	}


	for (int i = K; i < N; i++)
	{
		for (int j = MAX - 10; j >= 0; j--)
		{
			for (int k = 1; k <= 6; k++)
			{
				dp2[j + k] += dp2[j] / 6;
			}
			dp2[j] = 0;
		}
	}

	double ans = 0;
	for (int i = 0; i < MAX; i++)
	{
		for (int j = i + 1; j <MAX; j++)
		{
			ans += dp1[i] * dp2[j];
		}
	}
	printf("%.14f\n", ans);
}