#include<iostream>
#include<cstdio>
#include<vector>
#include<queue>
#include<utility>
#include<stack>
#include<algorithm>
#include<cstring>
#include<string>
using namespace std;

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