#pragma warning disable IDE1006
#pragma warning disable IDE0011
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Numerics;
using System.Text;
using static System.Convert;
using static System.Math;
using static Extentions;

class IO
{
    int idx;
    string[] line;

    public void R(params char[] sep) { line = Console.ReadLine().Split(sep); idx = 0; }
    public string S => line[idx++];
    public string[] Ss => line.Skip(idx++).ToArray();
    public char C => char.Parse(line[idx++]);
    public char[] Cs => line.Skip(idx++).Select(char.Parse).ToArray();
    public int I => int.Parse(line[idx++]);
    public int[] Is => line.Skip(idx++).Select(int.Parse).ToArray();
    public long L => long.Parse(line[idx++]);
    public long[] Ls => line.Skip(idx++).Select(long.Parse).ToArray();
    public double F => double.Parse(line[idx++]);
    public double[] Fs => line.Skip(idx++).Select(double.Parse).ToArray();
    public decimal D => decimal.Parse(line[idx++]);
    public decimal[] Ds => line.Skip(idx++).Select(decimal.Parse).ToArray();
    public BigInteger B => BigInteger.Parse(line[idx++]);
    public BigInteger[] Bs => line.Skip(idx++).Select(BigInteger.Parse).ToArray();

    public void Write<T>(params T[] xs)
    {
        Console.Write(xs.First());
        foreach (var x in xs.Skip(1)) Console.Write(" " + x);
        Console.WriteLine();
    }
    public void Write(params object[] xs)
    {
        Console.Write(xs.First());
        foreach (var x in xs.Skip(1)) Console.Write(" " + x);
        Console.WriteLine();
    }
}

static class Extentions
{
}

static class Program
{
    public static void Main()
    {
#if !DEBUG
        Console.SetOut(new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false });
#endif
        Solve(new IO());
        Console.Out.Flush();
    }

    public static void Solve(IO io)
    {
        var sw = new System.Diagnostics.Stopwatch();
        sw.Start();

        io.R();
        var n = io.I;
        io.R();
        var k = io.I;

        var rand = new Random();
        var won = 0;
        var times = 0;

        for (; sw.ElapsedMilliseconds < 4900; times++)
        {
            var taro = 0;
            for (var j = 0; j < k; j++) taro += rand.Next(4, 7);
            for (var j = 0; j < n - k; j++) taro += rand.Next(1, 7);

            var jiro = 0;
            for (var j = 0; j < n; j++) jiro += rand.Next(1, 7);

            if (taro > jiro) won++;
        }

        io.Write((double)won / times);
    }
}