#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf 1000000

int main(){
	
	int K;
	cin>>K;
	
	vector<double> dp(K+1,0),dpx(K+1,0);
	
	for(int i=K-1;i>=0;i--){
		for(int j=1;j<=6;j++){
			if(i+j>K)dpx[i] += 1.0/6.0;
			else{
				dp[i] += dp[i+j]/6.0;
				dpx[i] += dpx[i+j]/6.0;
			}
		}
		dp[i] += 1.0;
	}
	
	double X = 1.0 - dpx[0];
	double ans = dp[0];
	ans /= X;
	
	cout<<fixed<<setprecision(10)<<ans<<endl;
	
	
	return 0;
}