using System;

​

public class Program

{

    public static void Main()

    {

        Action<int, int> operation = default;

        operation = Add;

        operation.Invoke(1, 2);

        operation = Sub;

        operation.Invoke(1, 2);

    }

    private static void Add(int a, int b)

    {

        var sum = a + b;

        Console.WriteLine("Total Sum: {0}", sum);

    }

    private static void Sub(int a, int b)

    {

        var dif = a - b;

        Console.WriteLine("Total Sum: {0}", dif);

    }

}