using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.Specialized;
using System.Text;
using System.Text.RegularExpressions;
using System.Linq;


class Magatro
{
    static int N, K;
    static long[] Tcnt = new long[61], Zcnt = new long[61];
    static void Main()
    {
        N = int.Parse(Console.ReadLine());
        K = int.Parse(Console.ReadLine());
        calc();
        long cnt = 0;
        for(int i = 1; i < 60; i++)
        {
            for(int j = i + 1; j <= 60; j++)
            {
                cnt += Tcnt[j] * Zcnt[i];
            }
        }
        Console.WriteLine((double)cnt / (Tcnt.Sum() * Zcnt.Sum()));
    }
    static void calc()
    {
        int loop =(int) Math.Pow(6, N);
        for(int i = 0; i < loop; i++)
        {
            int c = i;
            int T=0, Z = 0;
            for(int j = 0; j < N; j++)
            {
                int d = c % 6;
                if (d == 0)
                {
                    d = 6;
                }
                Z += d;
                if (K - 1 > j)
                {
                    T += (3 + (d + 1) / 2);
                }
                else
                {
                    T += d;
                }
                c /= 6;
            }
            Tcnt[T]++;
            Zcnt[Z]++;
        }
    }
}