Tag - Filename format string help

Hi, just discovered this great tool earlier today.

I am trying to come up with a format string for Tag - Filename, but being a bit slow I can't figure out exactly how to do what I want.

Basically, what I want is for the filename to be 01 Blabla.mp3 if there is no discnumber, but if there is for example discnumber 1 tag I want the filename to be 101 Blabla.mp3.

What I've got so far is

$num(%discnumber%,)$num(%track%,2) %title%

Now I am guessing I have to use the if(x,y,z) and maybe some other functions, but I can't quite figure out how!

Any help would be greatly appreciated!

[$num(%discnumber%,1)]$num(%track%,2) %title%

Thanks, worked like a charm!