using System;
using System.Text.RegularExpressions;

public class Test
{
	public static void Main()
	{
		bool contains = Regex.IsMatch("Hello: Hello2", @"\bHello\b(?!:)");
		Console.WriteLine(contains);
		Console.WriteLine(Regex.IsMatch("Hello: Hello2", @"\bHello(?![:\w])"));
	}
}