using System;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        string text="AB4000-01-433593-1-1";

        // ^ start of word match any character A-Z or 0-9 until you hit a dash, then match any character except a dash. Capture in group 1 

        string regEx = @"^([A-Z,0-9]+-[^-]+)";

        Regex r = new Regex(regEx, RegexOptions.IgnoreCase);

        Match m = r.Match(text);

        if(m.Success)

        {

            Console.WriteLine(m.Groups[0]); 

        }

​

    }

}

​

​