#include <bits/stdc++.h>
using namespace std;
int main(){
	int i,h=0;
	cin>>i;
	for(;i>0;i--){
		h=h+i;
	}
	cout<<h;
} 
/**************************************************************
	Problem: 2100
	User: hongjiaming
	Language: C++
	Result: Accepted
	Time:40 ms
	Memory:2072 kb
****************************************************************/