//package yy;不能有

import java.util.*;

public class Main {//必须为Main

    public static void main(String[] args)

    {

        Scanner reader=new Scanner(System.in);

        int i,n;

        while(reader.hasNextInt())

        {

            n=reader.nextInt();

            int sum=0;

            for(i=1;i<=n;i++)

                sum+=i;

            System.out.println(sum+"\n\n");

        }

    }

}