Document Numbering

Hi all,

I would like of document numbering in following way

for a/r invoice

CompName/dept1/10-11/0001

CompName/dept2/10-11/0001

CompName/dept3/10-11/0001

Actually for each department. it is required to have different series and each will start from 1

when i am trying to achieve this in Document Numbering- i am getting overlaping error.

Regards

indrajit