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

double dp[MAX];
double dp2[MAX];
double p[MAX];
double p2[MAX];
int main(){
	int K;
	cin >> K;
	for (int i = 1; i <= K; i++)
	{
		dp[i] = dp2[i] = p[i] = p2[i] = 0;
		for (int j = 1; j <= 6; j++)
		{
			if (i - j == 0){
				p[i] += 1.0 / 6;
			}
			else if (i - j < 0){
				p2[i] += 1.0 / 6;
			}
			else{
				dp[i] += dp[i - j] * p[i - j] / 6;
				dp2[i] += dp2[i - j] * p2[i - j] / 6;
				p[i] += p[i - j] / 6;
				p2[i] += p2[i - j] / 6;
			}
		}
		dp[i] /= p[i];
		dp2[i] /= p2[i];
		dp[i] += 1;
		dp2[i] += 1;
	}
	double ans = dp[K] + dp2[K] / (p[K]) - dp2[K];
	printf("%.14f\n", ans);
}