#include <bits/stdc++.h>

using namespace std;

#define INF 2000000000
#define MOD 1000000007
typedef long long ll;
typedef pair<int, int> P;


int main()
{
	int n;
	cin >> n;
	int ret = 0;

	for (int i = 1; i <= n; i++) {
		ret += i;
	}
	cout << ret << endl;

}