#include <iostream>
#include <string>

using namespace std;

int main(int argc, char** argv)
{
	int n; cin >> n;

	long max = 0;
	for (int ii=0; ii<=n; ++ii) {
		long dw = (n-ii);
		long total = (ii * (dw+1)) + dw;
		max = (total>max) ? total : max;
	}
	cout << max << endl;
	return 0;
}