#include "bits/stdc++.h"
using namespace std;
#define MAX 500

double dp[MAX];

int main(){
	int K;
	cin >> K;
	dp[0] = 0;
	for (int t = 0; t < 10000; t++)
	{
		for (int i = 1; i <= K; i++)
		{
			double temp = 6;
			for (int j = 1; j <= 6; j++)
			{
				if (i - j < 0) temp += dp[K];
				else temp += dp[i - j];
			}
			dp[i] = temp / 6;
		}
	}
	printf("%.14f\n", dp[K]);
}