#include "bits/stdc++.h"

using namespace std;

void solve(void)
{
	int n, a, b, i;
	string s;

	//cout << "Hello World!" << endl;
	cin >> n;
	cout << (n + 1) * n / 2 << endl;
	/*
	cin >> a >> b >> s;
	cout << a + b << ' ' << s << endl;
	cin >> n;
	for (int j = 1; j <= n; j++)
	{
		if (j % 15 == 0)
			cout << "FizzBuzz";
		else if (j % 3 == 0)
			cout << "Fizz";
		else if (j % 5 == 0)
			cout << "Buzz";
		else
			cout << j;
		cout << endl;
	}
	cin >> n;
	long ans = 0;
	while (n--)
	{
		long x;
		cin >> x;
		ans += x;
	}
	cout << ans << endl;
	*/
}

int main(void)
{
	solve();
	//cout << "yui(*-v・)yui" << endl;
	return 0;
}