/**
 * Created by iyasuwatts on 10/17/17.
 */

import java.util.Scanner;

public class Main {

    public static void main(String[] args){

        Scanner scanner = new Scanner(System.in);

        int userInput = scanner.nextInt();
        int answer = 0;

        for(int i = 1;i <= userInput; i++) { 
            answer += i;
            

        }
        
        System.out.println(answer);
    }

}