#include <iostream>
#include <iomanip>
#include <vector>
using namespace std;
int main(){
	cout << fixed << setprecision(5);
	int K;
	cin >> K;
	vector<double> dp(K + 6, 0);
	for (int i = K - 1; i >= 0; i--){
		dp[i] = 1;
		for (int j = 1; j <= 6; j++){
			dp[i] += dp[i + j] / 6;
		}
	}
	cout << dp[0] << endl;
}