import java.util.Scanner;


public class Subtraction extends Calculator {




@Override
void sum()
{
   System.out.println("An abstract method");
    }

public static void main (String [] args){
    Calculator sub = new Subtraction();
    Scanner in = new Scanner(System.in);
    boolean repeat = true;
    System.out.println("Enter values:");
    while(repeat){

        try{
            int a= in.nextInt();
            int b= in.nextInt();
            System.out.println(+(a-b));
            repeat = false;

        }

        catch(Throwable t)
                {
                  System.out.println("Invalid Input!!!!!");
                  in.nextLine();
                  repeat = true;

                }

        finally{
            System.out.println("this is final block");
            sub.sum();
        }
    }
}


}

abstract class Calculator {

   abstract void sum ();
   public void info (){
           System.out.println("NON ABSTRACT METHOD");

}
}