#include <iostream>
#include <fstream>
#include <string>
#include <vector>

int main(void) {

	//std::ifstream inf("Text.txt");	std::cin.rdbuf(inf.rdbuf());

	int N = 0, sum = 0;
	std::cin >> N;

	for (int i = 0; i <= N; i++) {
		sum += i;
	}

	std::cout << sum << std::endl;

	return 0;
}