#include<bits/stdc++.h>
using namespace std;
int main(){
	int n,i,s=0;
	cin>>n;
	i=1;
	while (i<=n){
	s=s+i;
	i=i++;	
	}
	cout<<s;
	

}

/**************************************************************
	Problem: 1002
	User: wengsihan
	Language: C++
	Result: Time Limit Exceed
****************************************************************/