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

	return 0;
}

/**************************************************************
	Problem: 1002
	User: hbq
	Language: C++
	Result: Accepted
	Time:17 ms
	Memory:2072 kb
****************************************************************/