#include <iostream>
#include <cstdio>

using namespace std;

double saiki(double n){
	if(n==0) return 4.0;
	if(n==1) return 3.0;
	return (19*saiki(n-1) -12*saiki(n-2))/4.0;
}
int main(){
	int N;
	cin >> N;
	//cout << saiki(N) << endl;
	printf("%0.8f\n",saiki(N) );
	return 0;
}