package yukiCoder;

import java.util.Scanner;

public class No00480 {

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);
		int last = sc.nextInt();
		sc.close();

		int ans = 0;
		for (int i = 1; i <= last ; i++) {
			ans = ans + i;
		}
		System.out.println(ans);
	}

}