Count Formula in Business Objects

Good day,

Please help with a count formula for customer groups not logged on system. See table below.

Rule: If in a specific customer group one user (Group_001) has logged on to system that customer group is excluded from results.

         A customer group is considered having not logged on to system when no user within that customer group has logged on system.

A count of Customer Groups for below table must return 1 (Group 2)

I am using SAP Business Objects 4

Thank you.