#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint998244353;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf 1000000

int main(){
	
	int N;
	cin>>N;
	
	vector<double> ans(101);
	ans[0] = 4;
	ans[1] = 3;
	
	for(int i=2;i<=100;i++){
		ans[i] = ans[i-1] * 19 - ans[i-2] * 12;
		ans[i] /= 4.0;
	}
	
	cout<<fixed<<setprecision(15)<<ans[N]<<endl;
	
	return 0;
}