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


/**************************************************************
	Problem: 1002
	User: linweilun
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/