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

/**************************************************************
	Problem: 1002
	User: 21A
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/