import java.util.Scanner;

public class Sum {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int num = scanner.nextInt();
        int result = 0;

        if(num > 0) {
            for (int i = 1; i <= num; i++) {
                result += i;
            }
            System.out.println(result);
        } else {
            for (int i = num; i <=1 ; i++) {
                result += i;
            }
            System.out.println(result);
        }
    }
}