using System;
using static System.Console;

class Program
{
    static void Main()
    {
        var N = int.Parse(ReadLine());
        var K = int.Parse(ReadLine());
        
        var c = 0;
        var r = new Random();
        for (int i = 0; i < 1000000; i++)
        {
            var t = 0;
            var s = 0;
            for (int j = 0; j < N; j++) t += r.Next(6) + 1;
            for (int j = 0; j < N - K; j++) s += r.Next(6) + 1;
            for (int j = 0; j < K; j++) s += r.Next(3) + 4;
            if (t < s) c++;
        }
        
        WriteLine(c / 1000000.0);
    }
}