Changing disk number with Regex

Hi! I'm sure this is was mentioned before but i can't find it.

Some cd's come with the discknumber tag in the [discnumber/total discnumber] format.
I want to change it those cd's tag to only discnumber.

Any ideas?
Thank you for your time!

Create an action_
Action type: Guess values
Source format: %discnumber%
Guessing Pattern: %discnumber%/%dummy%

You really mean the discnumber or do you mean the tracknumber?

Discnumber! Sometimes they are like this 1/2 2/2 and i hate it xD

You would not believe how many threads there are that wish for a numbering assistant for the discnumber so that you get the total discnumber ... So throwing away existing data is always a dubious thing.

An alternative could also be:
Action of the type "Format value" for DISCNUMBER
Format String: $num(%discnumber%,2)