import java.util.Scanner;
public class HELLO {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner stdIn = new Scanner (System.in);
		int n = stdIn.nextInt();
		int total = 0;
		for(int i = 1; i<=n; i++) {
			total = total + i;
		}
		System.out.print(total);
	}

}