multiple forms(Invoice) page numbers using smartforms

HI

could any one help in calculating page number for multiple forms using smartforms.

Eg: iam printing 2 invoices, 1 invoice has 2 pages and other has 1 page.

          the form page numbers should be as page no./no. of pages 1/2, 2/2 for 1st invoice

                                                                                                1/1 for 2nd  invoice.