Lookup higest numer

Hello,

 i want to register al my cd's in a List, the problem is the cd's are numberd.
With that number i want te insert de cd in the list. to ignore the id's form
sharepoint i have made a new fiels Cd Code. This will ben trhe unique number for
a cd. Now im looking foor a auto lookup function that loopup that highest Cd
Code+1 and that is the deafult value for the field by inserting a new cd....

 does anyone know how to do this

 

many thnx!!!