#include<math.h>
#include<iostream>
using namespace std;
int main(){
	int n,ans;
	cin >> n;
	ans = (1 + n) * n / 2;
	cout << ans;
}
/**************************************************************
	Problem: 1002
	User: long
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/