//weekly CD
//https://www.hackerrank.com/contests/w14/challenges
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;

int func(int k){
	int sum = 0,cnt = 0;
	while(sum < k){
		sum += rand()%6+1;
		cnt++;
	}
	return cnt;
}

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

	ll sum = 0;
	for(int i=0;i<1e6;i++){
		sum += func(k);
	}
	cout << fixed << setprecision(5) << 1.*sum/1e6 << endl;
	return 0;
}