using System;
using System.Linq;

class Program
{
    public static void Main(string[] args)
    {
        var n = int.Parse(Console.ReadLine());
        var k = int.Parse(Console.ReadLine());
        var tDp = new double[n + 1, 6 * n + 1];
        var kDp = new double[n + 1, 6 * n + 1];

        tDp[0, 0] = 1;
        for (int t = 0; t < n; t++)
        {
            for (int p = 0; p <= 6*t; p++)
            {
                for (int i = 1; i <= 6; i++)
                {
                    tDp[t + 1, p + i] += tDp[t, p] * 1/6d;
                }                
            }
        }
        var r = n - k;
        for (int i = 0; i < 6*n+1; i++)
        {
            kDp[r, i] = tDp[r, i];
        }
        for (int t = r; t < n; t++)
        {
            for (int p = 0; p <= 6 * t; p++)
            {
                for (int i = 4; i <= 6; i++)
                {
                    kDp[t + 1, p + i] += kDp[t, p] * 1 / 3d;
                }
            }
        }
        double sum = 0;
        for (int i = 0; i <= 6*n; i++)
        {
            for (int j = 0; j < i; j++)
            {
                sum += kDp[n, i]*tDp[n, j];
            }               
        }
        Console.WriteLine(sum);        
    }
}