2 * (n - 1) + ((2 + (2 * n - 4)) * (n - 2) / 2)+n-1

#include <iostream>
using namespace std;

int main() {
	int n;
	cin >> n;
	cout << 2 * (n - 1) + ((2 + (2 * n - 4)) * (n - 2) / 2)+n-1;
	return 0;
}