#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[201];
int main(void)
{
	cin.tie(0);
	ios::sync_with_stdio(false);

	int n;

	cin >> n;

	double lo = 0;
	double hi = 1e9;
	for (int i = 0; i < 200; i++)
	{
		double mid = (lo + hi) / 2;
		dp[0] = 0;
		for (int j = 1; j <= n; j++)
		{
			dp[j] = 1;
			for (int k = 1; k <= 6; k++)
			{
				if (j - k >= 0)
				{
					dp[j] += (dp[j - k] / 6);
				}
				else
				{
					dp[j] += (mid / 6);
				}
			}
		}
		if (dp[n] > mid)
		{
			lo = mid;
		}
		else
		{
			hi = mid;
		}
	}

	cout << (lo + hi) / 2 << '\n';

	return 0;
}