#include<iostream>
#include<algorithm>

using namespace std;

double dp[2][216], res;
int l, k;
int main(){
	dp[0][0] = 1;
	cin >> k;
	for(int i = 1, id = 1;i < 108000;i++,id ^= 1){
		for(int j = 0;j <= k;j++)dp[id][j] = 0;
		for(int j = 0;j <= k;j++){
			for(int l = j+1;l <= j+6;l++){
				dp[id][l>k?0:l] += dp[!id][j] /6.0;
			}
		}
		res += dp[id][k]*i;
		dp[id][k] = 0;
	}
	cout << res << endl;
	return 0;
}