package yukicoder.tutorial.sum.bywhitespace;

import java.util.Scanner;
import java.util.stream.IntStream;

public class Main {

	@SuppressWarnings("resource")
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int length = sc.nextInt();
		System.out.println(IntStream.range(0, length).sum());
	}
}