#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <utility>
#include <iomanip>
using namespace std;

int main(void) {
	int n, ans = 0;
	cin >> n;
	for (int i = 1; i <= n; i++)
		ans += i;
	cout << ans << endl;
	return 0;
}