import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = Integer.parseInt(sc.next());
		int sum =0;
		for(int i = 0; i<n; i++) {
			sum += i+1;
		}
		System.out.println(sum);
	}
}