package com.company;

import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int value = scanner.nextInt();
        double left = 0;
        double right = 1e10;
        double middle = (left + right) / 2.0;
        for(int i = 0 ; i < 200;i++)
        {
            double[] dp = new double[value+1];
            middle = (left + right) / 2.0;
            for(int k = value-1;k >= 0;k--)
            {
                double sum = 1;
                for(int m = 1;m <=6;m++)
                {
                    if(k + m > value)
                    {
                        sum += middle / 6.0;
                    }
                    else
                    {
                        sum += dp[k+m] / 6.0;
                    }
                }
                dp[k] = sum;
            }
            if(dp[0] < middle)
            {
                right = middle;
            }
            else
            {
                left = middle;
            }
        }
        System.out.println(middle);
    }
}