Maybe John is a recently assembled robot, or he is a human who was grown on a lab at the basement. Maybe he was kept in that store for all his life. Maybe Jack entered the store, decided he was now a changed man, called himself John and we define John as Jack from that point on. This is not that different from how a human egg becames a new person. Maybe we should see the city as a giant store. Maybe this all takes place in SCP3008.
And it just ocurred to me. The correct answer is zero because it is never stated that John, despite needing bottles from the store, has to do it himself.
Who is smarter now, me or the test?