#include <iostream>
#include <cstdint>

using namespace std;

int main()
{
	cin.tie(nullptr);
	ios::sync_with_stdio(false);

	uint64_t N;
	cin >> N;

	if (N & UINT64_C(1))
		cout << (N + 1) / 2 * N << '\n';
	else
		cout << N / 2 * (N + 1) << '\n';

	return 0;
}