#include <bits/stdc++.h>

using namespace std;

int K;

double solve(double ans) {
	double dp[205] = {};
	for (int i = K - 1; i >= 0; i--) {
		for (int j = 1; j <= 6; j++) {
			if (i + j > K) dp[i] += ans;
			else dp[i] += dp[i + j];
		}
		dp[i] /= 6;
		dp[i]++;
	}
	return dp[0];
}

int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);
	cin >> K;
	double ok = 0, ng = 300;
	for (int loop = 0; loop < 30; loop++) {		
		double mid = (ok + ng) / 2;
		if (solve(mid) >= mid) ok = mid;
		else ng = mid;
	}
	cout << ok << endl;
	return 0;
}