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];
    const int MAX = 2000000;
    static void Main()
    {
        N = int.Parse(Console.ReadLine());
        K = int.Parse(Console.ReadLine());
        int cnt = 0;
        Random rnd = new Random();
        for(int i = 0; i < MAX; i++)
        {
            int taro = 0, ziro = 0;
            for(int j = 0; j < N; j++)
            {
                ziro += rnd.Next(1, 6+1);
                if (j <= K - 1)
                {
                    taro += rnd.Next(4, 6+1);
                }
                else
                {
                    taro += rnd.Next(1, 6+1);
                }
            }
            if (taro > ziro)
            {
                cnt++;
            }
        }
        Console.WriteLine((double)cnt / MAX);
    }

}