#include <map>
#include <set>
#include <list>
#include <cmath>
#include <ctime>
#include <deque>
#include <queue>
#include <stack>
#include <bitset>
#include <cstdio>
#include <limits>
#include <vector>
#include <cstdlib>
#include <numeric>
#include <sstream>
#include <iostream>
#include <algorithm>
#include <functional> 
#include <iomanip>
#include <unordered_map>
#include <memory.h>
#include <unordered_set>
#include <fstream>
#include <random>

using namespace std;

long double dp[21];
int main(void)
{
	cin.tie(0);
	ios::sync_with_stdio(false);

	dp[1] = 1;
	for (int i = 2; i <= 20; i++)
	{
		double sum = 1;
		for (int j = 1; j <= 6; j++)
		{
			if (i - j >= 1)
			{
				sum += (dp[i - j] / 6);
			}
		}
		dp[i] = sum;
	}

	cout << fixed;
	cout.precision(6);

	int n;

	cin >> n;

	cout << dp[n] << '\n';

	return 0;
}