abstract class Arithmetic
{
    public int add(int a, int b)
    {
        int c = a + b;
        return c;
    }
    public void display(int c)
    {
        Console.Write("Addition " + c);
    }
}

class Program : Arithmetic
{
    public static void Main(String[] args)
    {
        Program p = new Program();
        int addition = p.add(10, 10);
        p.display(addition);
    }
}

kodingwindow@kw:~/csharp$ dotnet run
Addition 20
kodingwindow@kw:~/csharp$ 

WhiteBank wb = new WhiteBank();
GreenBank gb = new GreenBank();
wb.Bonus();
gb.Bonus();

abstract class Bank
{
    public abstract void Bonus();
}
class WhiteBank : Bank
{
    public override void Bonus()
    {
        Console.WriteLine("Festival Bonus: WhiteBank 1500");
    }
}
class GreenBank : Bank
{
    public override void Bonus()
    {
        Console.Write("Festival Bonus: GreenBank 500");
    }
}

kodingwindow@kw:~/csharp$ dotnet run
Festival Bonus: WhiteBank 1500
Festival Bonus: GreenBank 500
kodingwindow@kw:~/csharp$