8393 : 합

import java.util.Scanner;

public class Main {
	public static void main(String[] args) throws Exception {

		Scanner sc = new Scanner(System.in);
		int num = sc.nextInt();
		int sum = 0;
		for (int i = 1; i <= num; i++) {
			sum += i;
		}
		System.out.println(sum);

	}
}