#include<bits/stdc++.h>
using namespace std;
int main(){
	int n;
	cin >> n ;
	cout << n * (n + 1)/2;
	return 0;

}

/**************************************************************
	Problem: 1002
	User: Hawthorne
	Language: C++
	Result: Accepted
	Time:29 ms
	Memory:2072 kb
****************************************************************/