using System;

using System.Text.RegularExpressions;

​

public class Program

{

    public static void Main()

    {

        var input = "Old Macdonald had a farm and on";

        var regex = new Regex(@"(?<=Macdonald\s).*(?=\sand)", RegexOptions.Compiled | RegexOptions.IgnoreCase);

        var match = regex.Match(input);

        if (match.Success)

        {

            Console.WriteLine(match.Value);

        }

        else

        {

            Console.WriteLine("No farms for you");

        }

    }

}