#include <iostream>
#include <algorithm>
#include <sstream>
#include <cmath>

using namespace std;

int main(int argc, char *argv[])
{
	cout.precision(12);
	int N;
	cin >> N;
	long double A[101] = {};
	long double B = 1LL << 50;
	B *= B;
	A[0] = B * 4, A[1] = B * 3;
	for (int i = 2; i <= N; ++i) {
		A[i] = (19 * A[i - 1] - 12 * A[i - 2]) * 0.25;
	}
	cout << (A[N] / B) << endl;
	return 0;
}