using System;
using System.Collections.Generic;

public class A
{
  public virtual int Calculate(int num1, int num2)
  {
    return num1 num2;
  }
}

public class B : A
{
  public override int Calculate(int num1, int num2)
  {
    return num1 - num2;
  }
}
class C : B
{
  public override int Calculate(int num1, int num2)
  {
    return num1 - num2;
  }

static void Main()
{
  B obj = new B();
  int answer = obj.Calculate(24, 12);
}