/* package whatever; // don't place package name! */

import java.util.*;
import java.lang.*;
import java.io.*;

/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
       Scanner scan = new Scanner(System.in);
        String str = scan.nextLine();

        int n = Integer.parseInt(str);
        int sum = 0;

        for(int i=1; i<=n; i++) {
            sum += i;
        }

        System.out.println(sum);
        scan.close();
	}
}