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

using namespace std;

const int MAX_ROLL = 1e8;

int main() {
	int k;
	cin >> k;

	int seed = 0;
	mt19937 mt(seed);
	uniform_int_distribution<> dice(1, 6);


	int sum = 0;
	int start = 0;
	long long success = 0;
	for (int i = 0; i < MAX_ROLL; i++) {
		sum += dice(mt);

		if (sum == k) {
			success++;
			sum = 0;
		} else if (sum > k) {
			sum = 0;
		}
	}

	double ans = success != 0 ? 1.0 * MAX_ROLL / success : MAX_ROLL;
	printf("%.6f\n", ans);

	return 0;
}