import javax.servlet.*; 
import javax.servlet.http.*;
import java.io.*; 

public class Unicorn extends HttpServlet {
  public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException {
    response.setContentType("text/html"); 
    PrintWriter out = response.getWriter();
    // out.println("Hello."); 

    String message = request.getParameter("message"), 
           n1 = request.getParameter("n1"), 
           n2 = request.getParameter("n2"), 
           answer = request.getParameter("answer");
    if (message == null) {
      message = "Welcome."; 
      n1 = (int)(Math.random() * 100 - 50) + "";
      n2 = (int)(Math.random() * 100 - 50) + "";
    } else {
      int key = Integer.parseInt(request.getParameter("n1")) + 
                Integer.parseInt(request.getParameter("n2")); 
      if (Integer.parseInt(answer) == key) {
        message = "That's right!"; 
      } else {
        message = "No, the right answer would've been " + key; 
      } 
      n1 = (int)(Math.random() * 100 - 50) + "";
      n2 = (int)(Math.random() * 100 - 50) + "";
    } 

    out.println(

"<form>" + 
  message + "<p>" + 
  "What is " + n1 + " + " + n2 + "? <input type=text name=answer size=4> <p>" + 
  "Press <input type=submit value=Proceed> to continue. " + 
  "<input type=hidden name=n1 value=" + n1 + ">" + 
  "<input type=hidden name=n2 value=" + n2 + ">" + 
  "<input type=hidden name=message value=" + message + ">" +     
"</form>"

    ); 
  }   
}