using System;

using System.Linq;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        var str = "I have asked the question in StackOverflow. Therefore i can expect answer here.";

        var numMatches = Regex.Matches(str.ToUpper(), "THE")

            .Cast<Match>()

            .Count(match => 

                (match.Index == 0 || str[match.Index - 1] == ' ') && 

                (match.Index + match.Length == str.Length || 

                    !Regex.IsMatch(

                        str[match.Index + match.Length].ToString(),

                        "[a-zA-Z]")));

        Console.WriteLine(numMatches);

    }

}