#include <iostream>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <stdio.h>
#include <cstdio>
using namespace std;
int main()
{
	int N,sum=0;
	cin>>N;
	for (int i=1; i<=N; i++)
	{
		sum=sum+i;
	}
	cout<<sum<<endl;
}