import java.util.Scanner;

/** Let's use a stack to see if an expression has matching parentheses.
 */
public class Paren
{
  public static void main(String [] args)
  {
    System.out.printf("Enter an expression:  ");
    Scanner kbd = new Scanner(System.in);
    String line = kbd.nextLine();
    LinkedListStack stack = new LinkedListStack();

    // Each time we see a '(', push it on the stack.
    // Each time we see a ')', pop its corresponding '(' from the stack.
    // For other characters, we just ignore.
    // Reject input when 1 of 2 cases occurs:
    //   The stack is not empty when finished with input.
    //   Try to pop from empty stack (right with no left).

    boolean goodInput = true;

    for (int i = 0; i < line.length(); ++i)
    {
      char c = line.charAt(i);
      if (c == '(')
        stack.push(new Character (c));
      else if (c == ')')
      {
        // When we see the ')', the stack must not be empty.
        if (stack.size() == 0)
        {
          goodInput = false;
          break;
        }
        stack.pop();
      }
      else
        continue;
    }

    // Stack should be empty when we're done reading input.
    if (stack.size() > 0)
      goodInput = false;

    // output
    System.out.printf("Your input is %s\n", goodInput ? "good" : "bad");
  }
}