#define _USE_MATH_DEFINES
#include <algorithm>
#include <cstdio>
#include <functional>
#include <iostream>
#include <cfloat>
#include <climits>
#include <cstring>
#include <cmath>
#include <map>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <time.h>
#include <vector>
using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> i_i;
typedef pair<ll, int> ll_i;
typedef pair<double, int> d_i;
typedef pair<ll, ll> ll_ll;
typedef pair<double, double> d_d;
struct edge { int u, v; ll w; };

ll MOD = 1000000007;
ll _MOD = 1000000009;
double EPS = 1e-10;

int main() {
	ll K; cin >> K;
	if (K < 1000) {
		vector<double> dp(K + 1), _dp(K + 1);
		for (int i = 1; i <= K; i++) {
			for (int j = 1; j <= 6; j++) {
				dp[i] += (i >= j ? dp[i - j] : 0);
				_dp[i] += (i >= j ? _dp[i - j] : 1);
			}
			dp[i] = dp[i] / 6 + 1;
			_dp[i] = _dp[i] / 6;
		}
		printf("%.15f\n", dp[K] / (1 - _dp[K]));
	}
	else {
		cout << K + 1 << ".666666666666666666666666666666666" << endl;
	}
}