Group Membership change - workflow.

Hi Guys. 

I need to setup an email alert when a group member is either added or removed. I have created a workflow but a tad stuck. 

I dont want all group membership changes to generate an alert but just some specific groups. 

What i have is

Operation that starts this workflow: Add or remove member from group

Target object type: Group

Initiator Conditions

Any User  Active Directory

What i am stuck on is setting the workflow up to only look at a specific group? 

Any ideas? 

Thanks in advance,