SSRS + assign numbers to parent item

Hi,

we are using SSRS 2005. The report is hirarchy report - only parent and child. i am getting data all in one datatable and using 1 field (say table1.mainID) as parent group field. Initial load of report is shown as expanded report with all parent and children showing up. This reports is shown in asp.net applciation using report viewer control.

Now user wants to number the parents, so that they know how many parents or mainID have come into the system. That is they want it like this:

1  parentID

      child1

      child2

2 ParentID

      child1

3 ParentID

     child1

     child2

     child3

There is no meaning for this 1,2,3. Just they want to know there are 4 parents or 5 parents or 6parents showing up on report. How to achieve this. I can do it in database also.

I appreciate your response.

Thanks,

Spunny