#include <iostream>
#include <cstdio>
using namespace std;
typedef long long ll;

int dice[6] = {1, 2, 3, 4, 5, 6};
int cheat[6] = {4, 4, 5, 5, 6, 6};

ll dp1[15][100], dp2[15][100];

int main(){
    int N, K;
    cin >> N >> K;
    
    const int M = 6 * N;
    
    dp1[0][0] = 1;
    for(int i=0;i<N;i++){
        for(int sum=0;sum<=M;sum++){
            for(int j=0;j<6;j++){
                dp1[i+1][sum + dice[j]] += dp1[i][sum];
            }
        }
    }
    
    dp2[0][0] = 1;
    for(int i=0;i<N;i++){
        for(int sum=0;sum<=M;sum++){
            for(int j=0;j<6;j++){
                dp2[i+1][sum + (i < K ? cheat[j] : dice[j])] += dp2[i][sum];
            }
        }
    }
    
    ll sum1 = 0;
    ll sum2 = 0;
    ll win = 0;
    
    for(int sum=0;sum<=M;sum++){
        win += sum1 * dp2[N][sum];
        sum1 += dp1[N][sum];
        sum2 += dp2[N][sum];
    }
    
    ll total = sum1 * sum2;
    printf("%.10f\n", (double)win / total);

    return 0;
}