Numbering scheme from certain point

How would I go about numbering from a certain number?

I use this $num(%_counter%,2) - %artist% - %title% to number from 1 to 30 (assuming I have 30 songs in my playlist).

However, lets say I want to add 20 more songs to the list. So I want the next 20 songs to follow the same naming scheme in consecutive order. So these 20 songs would continue with 31, 32, 33, 34, etc….

Is there a command that I can set to do this? or would i have to put all 50 songs in a folder and start all over in numbering scheme?

You could use Convert -> Autonumbering Wizard and set your TRACK with
Begin at tracknumber: 31

Then use something like
$num(%track%,2) - %artist% - %title%

Or you could try to add your start value manually to %_counter%

Use $num($add(%_counter%,30),2)

Thank you very much. This is exactly what I was looking for.