import java.util.Scanner;

public class No480 {

	public static void main(String[] args) {
		Scanner s = new Scanner(System.in);
		String N = s.nextLine();
		s.close();
		
		int i = 1,count=0;
		for(i = 1;i <= Integer.parseInt(N);i++){
			count += i;
		}
		
		System.out.println(count);

	}

}