package hello;

import java.util.Scanner;

public class HelloWorld {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		//        String s = sc.next();
		int a = sc.nextInt();
		int sum = 0;
		for (int i = 0; i < a; i++) {
			sum += i + 1;
		}
		//		System.out.println("Hello World!");
		System.out.println(sum);
	}

}