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

class Program
{
    static void Main()
    {
        new Magatro().Solve();
    }
}

struct S
{
    public bool[] Use;
    public long Price;
    public S(long p, bool[] u)
    {
        Price = p;
        Use = u;
    }
}

class Magatro
{
    private int K;

    private double[] D = new double[201];

    private void Scan()
    {
        K = int.Parse(Console.ReadLine());
    }

    private bool Func(double d)
    {
        double[] dp = new double[K + 1];
        dp[K] = 0;
        for (int i = K - 1; i >= 0; i--)
        {
            dp[i] = 1;
            for (int j = 1; j <= 6; j++)
            {
                if (i + j > K)
                {
                    dp[i] += d / 6;
                }
                else
                {
                    dp[i] += dp[i + j] / 6;
                }
            }
        }
        return d >= dp[0];
    }

    public void Solve()
    {
        Scan();
        double min = 0;
        double max = 10000;
        for (int n = 0; n < 100; n++)
        {
            double mid = (min + max) / 2;
            if (Func(mid))
            {
                max = mid;
            }
            else
            {
                min = mid;
            }
        }
        Console.WriteLine(max);
    }
}