#include "bits/stdc++.h"
using namespace std;
#define MAX 1005

double dp[MAX];

int main(){
	for (int i = 1; i < MAX; i++)
	{
		for (int j = 1; j <= min(6, i - 1); j++)
		{
			dp[i] += dp[i - j] / 6;
		}
		dp[i] += 1;
	}
	int N;
	cin >> N;
	printf("%.14f\n", dp[N]);

}