import java.util.Scanner ;
public class Oneton {
	public static void main(String[]args) {

		Scanner stdIn = new Scanner(System.in);
		int a = stdIn.nextInt();
		int sum;

		sum = 0;

		for(int i=0; i < a ;i++) {
			sum += i+1	;
		}

		System.out.println(sum);


	}

}