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

using namespace std;

const int max_play = 1e7;

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

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

	vector<int> count(21, 0);
	int sum, roll;
	int play = 0;
	while (play < max_play) {
		sum = 0;
		roll = 0;
		while (sum < k) {
			sum += dice(mt);
			roll++;
		}
		count[roll]++;
		play++;
	}

	int total  = 0;
	for (int i = 0; i < count.size(); i++) {
		total += i * count[i];
		// cout << count[i] << endl;
	}

	double ans = 1.0 * total / max_play;
	printf("%.6f\n", ans);

	return 0;
}