#include<iostream>
#include<algorithm>
using namespace std;
double dp[21];
int main(){
	int k; cin >> k;
	for (int i = 1; i <= k; i++){
		for (int j = 1; j <= min(6, i - 1); j++){
			dp[i] += dp[i - j] / 6;
		}
		dp[i] += 1;
	}
	cout << dp[k] << endl;
	return 0;
}