#include<bits/stdc++.h>
using namespace std;
int main(){
	int n,l;
	cin>>n;
	l=(1+n)*n/2;
	cout<<l;
}
/**************************************************************
	Problem: 1002
	User: wangyiyang
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/