import java.util.*;

/**
 Illustrates the use of a boolean variable to control loop ending.
*/
public class BooleanDemo
{
    public static void main(String[] args)
    {
        System.out.println("Enter nonnegative numbers.");
        System.out.println("Place a negative number at the end");
        System.out.println("to serve as an end marker.");
        int next, sum = 0;
        boolean numbersLeft = true;
        Scanner keyboard = new Scanner(System.in);
        while (numbersLeft)
        {
            next = keyboard.nextInt( );
            if (next < 0)
                 numbersLeft = false;
            else
                 sum = sum + next;
       }
        System.out.println("The sum of the numbers is " + sum);
    }
}