#include<iostream>
using namespace std;

#pragma warning(push)
#pragma warning(disable: 4996)

int N;

int main()
{
	//freopen("office.in", "r", stdin);
	//freopen("office.out", "w", stdout);

	cin >> N;

	if (N == 1 || N == 2)
	{
		cout << 16 << endl;
	}
	else
	{
		cout << 15 + ((N - 1)* N / 2) - N << endl;
	}

	return 0;
}

#pragma warning(pop)