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


		
	return 0;
}
/**************************************************************
	Problem: 1002
	User: cyp
	Language: C++
	Result: Accepted
	Time:7 ms
	Memory:2072 kb
****************************************************************/