#include <iostream>
using namespace std;

int main()
{
	int n, in, a;
	while (cin >> in){
		n = 0;
		if (in > 2){
			for (int i = 2; i <= in; i++){
				if (i == 2) a = 4;
				else a += i;
			}
			n = n + a;
		}
		else n = in * 2;

		cout << n << endl;
	}
	return (0);
}