using System;
 
class Program
{
    static void Main()
    {
        int n = int.Parse(Console.ReadLine());
        int k = int.Parse(Console.ReadLine());
 
        var dp = new long[n+1, 6*n+1];
        dp[0, 0] = 1;
 
        for (var i = 0; i < n; ++i)
        {
            for (var j = 0; j <= 6*n; ++j)
            {
                if (dp[i, j] != 0)
                {
                    for (var l = 1; l <= 6; ++l)
                    {
                        dp[i+1, j+l] += dp[i, j];
                    }
                }
            }
        }
 
        var dp2 = new long[n+1, 6*n+1];
        dp2[0, 0] = 1;
 
        for (var i = 0; i < k; ++i)
        {
            for (var j = 0; j <= 6*n; ++j)
            {
                if (dp2[i, j] != 0)
                {
                    for (var l = 4; l <= 6; ++l)
                    {
                        dp2[i+1, j+l] += dp2[i, j] * 2;
                    }
                }
            }
        } 
        for (var i = k; i < n; ++i)
        {
            for (var j = 0; j <= 6*n; ++j)
            {
                if (dp2[i, j] != 0)
                {
                    for (var l = 1; l <= 6; ++l)
                    {
                        dp2[i+1, j+l] += dp2[i, j];
                    }
                }
            }
        }
 
        long cnt = 0;
        double ans = 0;
        var x = Math.Pow(6, n*2);
 
        for (var i = n+1; i <= 6*n; ++i)
        {
            cnt += dp[n, i-1];
            ans += cnt * dp2[n, i] / x;
        }
 
        Console.WriteLine(ans);
    }
}