#include <iostream>
#include <cstdio>
#include <vector>
#include <algorithm>
#include <utility>

using namespace std;

int k;
vector<long long> plays;
vector<long long> pow6;

void dfs(int x, int times) {
	if (x >= k) {
		plays[times] += pow6[k - times];
		return ;
	}

	for (int i = 1; i <= 6; i++) {
		dfs(x + i, times + 1);
	}
}

int main() {
	cin >> k;

	plays.assign(21, 0);
	pow6.assign(21, 0);

	pow6[0] = 1;
	for (int i = 1; i <= 20; i++) {
		pow6[i] = pow6[i - 1] * 6;
	}

	dfs(0, 0);

	long long sum = 0;
	for (int i = 0; i < plays.size(); i++) {
		sum += plays[i] * i;
	}

	double ans = 1.0 * sum / pow6[k];
	printf("%.5f\n", ans);
	return 0;
}