/**
 * Created by Mexi 05/29/2018.
 */
import java.util.Scanner;
import java.lang.Math;
public class Main {
       
    public static void main(String[] args){
        Scanner in = new Scanner(System.in);
        System.out.println("Please input a number!");
        int n = Integer.parseInt(in.nextLine());
        int sum = 0;
        for (int i=0;i<=n;i++){
             sum = sum +i;
            
            }
        System.out.println(sum);
        
        
    }
}