#include <bits/stdc++.h>
using namespace std;
int main (){
  int a,b,s=0;
  cin>>a;
  for(b=1;b<=a;b++) s=s+b;
  cout<<s;

}

/**************************************************************
	Problem: 1002
	User: wtq001
	Language: C
	Result: Compile Error
****************************************************************/