#include<iostream>
#include<vector>
#include<algorithm>
#include<functional>
#include<set>
#include<map>
#include<string>
#include<iomanip>
#include<cmath>

int main()
{
	double N;
	std::cin >> N;
	std::cout << std::setprecision(15) << 4 * std::pow(0.75, N) << std::endl;
}