#include <bits/stdc++.h>
#include <boost/multiprecision/cpp_int.hpp>
using namespace std;
using namespace boost::multiprecision;

int main()
{
	cpp_int N, res = 0;
	cin >> N;
	for (int i = 1; i <= N; i++) {
		res += i;
	}
	cout << res << endl;
	return 0;
}