Multiple predecessors

[Mark D]

I have a project to install software at 30 + sites. each site is listed as a task with the exact same subtasks. The deployment plan calls to start the first 3 sites concurrently and then as any one of the sites completes a pre determined task the next site (site 4) can begin, and so on. For example the first 3 sites begin, site 2 reaches the pre determined task so site 4 can begin, then site 1 completes the predetermined task so now site 5 can begin, and so on.