#define _USE_MATH_DEFINES
#include <algorithm>
#include <cstdio>
#include <fstream>
#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; double w; };

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

int main() {
	int K; cin >> K;
	int x = 0;
	for (int t = 0; t < 1000000; t++) {
		int sum = 0;
		int i;
		for (i = 1; ; i++) {
			sum += rand() % 6 + 1;
			if (sum >= K) break;
		}
		x += i;
	}
	printf("%.10f\n", x / 1000000.0);
}