Hello @Short I would like to help you , can you Share the original name of one docuemnt or the origial text that you are proccesing , just to create the correct Regex
Try this (6000).+
This matches the string (6000) literally followed by any number of characters.
Also, for further help with regexes, this website is very good at explaining your regex.
Lastly,
You can also use String.StartsWith() method to solve your current problem, you may not need regex at all.
Here is the documentation with examples: