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

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