import java.util.Scanner;
/**
 * Created by iyasuwatts on 10/17/17.
 */

//Elliott Stansbury edit
public class Main {

    public static void main(String[] args){
    Scanner reader = new Scanner(System.in);  // Reading from System.in
    System.out.println("Enter a number: ");
    int n = reader.nextInt();
    
    int Sum = n * (n+1)/2;
    
    System.out.println(Sum);
    
    }
}