import java.util.Scanner;
public class Main {
	public static void main(String[] args) {
		int ans = 0;
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();

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