#include <bits/stdc++.h>
#define rep(i, a) for (int i = 0; i < (a); i++)
#define rep2(i, a, b) for (int i = (a); i < (b); i++)
#define repr(i, a) for (int i = (a) - 1; i >= 0; i--)
#define repr2(i, a, b) for (int i = (b) - 1; i >= (a); i--)
using namespace std;
typedef long long ll;
const ll inf = 1e9;
const ll mod = 1e9 + 7;

int K;
double dp[200];

bool ok(double m) {
	memset(dp, 0, sizeof(dp));
	for (int i = 1; i <= K; i++) {
		for (int j = 1; j <= 6; j++) {
			if (i - j < 0) dp[i] += m;
			else dp[i] += dp[i - j];
		}
		dp[i] = dp[i] / 6.0 + 1;
	}
	return dp[K] >= m;
}

int main() {
	cin >> K;

	double l = 0;
	double r = 1e9;
	rep (ii, 121) {
		double m = (l + r) / 2;

		if (ok(m)) {
			l = m;
		} else {
			r = m;
		}
	}

	printf("%.20f\n", r);

	return 0;
}