using System;

public class Program

{

    class BillingSystem

    {

        public void ShowEmployeeList()

        {

            Console.WriteLine("Return List of all the Employees from 'BillingSystem'");

        }

    }

    class ThirdPartyBillingSystem

    {

        public string ShowEmployeeList()

        {

            return "Return List of all the Employees from 'ThirdPartyBillingSystem'";

        }

    }

    // Now let us write the adapter interface for our concrete adapters

    interface IAdapter

    {

        void Do();

    }

    // Adapter for BillingSystem library

    class BillingSystemAdapter : IAdapter

    {

        private readonly BillingSystem _billingSystem;

        public BillingSystemAdapter()

        {

            _billingSystem = new BillingSystem();

        }

        public void Do()

        {

            _billingSystem.ShowEmployeeList();

        }

    }

    //Adapter for ThirdPartyBillingSystem library

    class ThirdPartyBillingSystemAdapter : IAdapter

    {

        private readonly ThirdPartyBillingSystem _thirdPartyBillingSystem;

        public ThirdPartyBillingSystemAdapter()

        {

            _thirdPartyBillingSystem = new ThirdPartyBillingSystem();

        }

        public void Do()

        {

            Console.WriteLine(_thirdPartyBillingSystem.ShowEmployeeList() + "\n");

        }

    }

    public static void Main()

    {

        IAdapter adapter = null;

        adapter = new BillingSystemAdapter();

        adapter.Do();

        adapter = new ThirdPartyBillingSystemAdapter();

        adapter.Do();

    }

}