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







/**************************************************************
	Problem: 1002
	User: zhangchenhao
	Language: C++
	Result: Accepted
	Time:6 ms
	Memory:2072 kb
****************************************************************/