#include <bits/stdc++.h>

using namespace std;

double dp[205];

int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);
	int K;
	cin >> K;
	dp[0] = 300;
	double ans = dp[0];
	for (int loop = 0; loop < 10000; loop++) {		
		for (int i = K - 1; i >= 0; i--) {
			dp[i] = 0.0;
			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]++;
		}
		ans = dp[0];
	}
	cout << ans << endl;
	return 0;
}