Number of registrations per user.

I am trying to configure views to show users with a certain number of registrations. For example, users should register for three sessions.
I would like to create a view that shows users with less than three registrations.
I would like to create that counts the number of registrations per users. I can return a view that shows registrations for a user but can't figure out how to get the count. Any pointers would be greatly appreciated.