Alpha Numeral Generating Code

Hi,
In the attached model, I am trying to create an automatic Alpha Numeral Job code matrix Budget.
The Alpha numeral consist of 1st three letters of department- 1st three letter of project and then a number.
The number for different months starts with 1 again how can I have a continuation of the number from the previous month for e.g for department System and Project name System atacenter the Jobcode ends with Sys-Data4. [u:1di9439x]I want the jobcode for November to start from Sys-Data5[/u:1di9439x].