/**
 * Created by iyasuwatts on 10/17/17.
 */
import java.util.*;
public class Main {

    public static void main(String[] args){
        Scanner input = new Scanner(System.in);
        int number = input.nextInt();
        int sum=0;
       
        for (int x=1; x<=number; x++){
         sum += x;
        }
        System.out.println(sum);
    }
}