Crystal Reports Summary Total on Max Timestamp

Message

Hi,
I have a table consisting of the below columns. I need to sum up all Qty Passed per Product. This is simple. I just need to create a group and Insert Group Summary on Qty Passed. Now comes the tricky part. I also need to sum up all Qty Failed where we have the maximum timestamp for each TIS #. In this case, it is 5 + 65 = 70.  
Appreciate any thoughts on how to do this computation.

Data
----
Product  TIS#   Qty Passed  Qty Failed     Timestamp
-------+------+-----------+------------+-------------------------
ABCD      01          100           10    02/01/2008 11:00:00 AM
ABCD      01           50            5    02/01/2008 11:30:00 AM  <-- Max Timestamp for TIS #1 
ABCD      02           20           25    02/01/2008 08:00:00 AM
ABCD      02           30           35    02/01/2008 08:30:00 AM
ABCD      02           40           65    02/01/2008 09:00:00 AM  <-- Max Timestamp for TIS #2

Result
------
Product  Qty Passed   Qty Failed 
-------+------------+----------------------
ABCD         240             70   (5 + 65)