import java.util.Scanner;

public class var_27_task_2 {

    public static void main(String[] args) {

        Scanner scanner = new Scanner(System.in);

        boolean isIncorrect;
        int n = 0;

        do {
            System.out.print("Enter the value of n : ");
            isIncorrect = false;
            try {
                n = Integer.parseInt(scanner.nextLine());
            } catch (NumberFormatException exception) {
                isIncorrect = true;

                System.err.println("Input Error. Check if the data is correct.");
            }


            if (!isIncorrect && (n <= 0)) {
                isIncorrect = true;

                System.err.println("Input Error. Check if the data is correct.");
            }
        } while (isIncorrect);

        scanner.close();

        int SumOfNumbers = 0;
        int i;

        for (i = 1; i<=n; i++){
            SumOfNumbers += ((i-1)+i);
        }

        System.out.println("Sum of all numbers = " + SumOfNumbers);

    }

}