import java.util.Scanner;

public class Gokei {

	public static void main(String[] args) {
		Scanner s = new Scanner(System.in);
		int i = 0 , a = s.nextInt() , sum = 0;
		s.close();
		while(i <= a){
			sum += i++;
		}
		System.out.println(sum);
	}

}