How should I split 9 nights among Berlin, Prague, and Krakow?

I was originally planning 5 nights in Berlin and 4 nights in Krakow, but I really want to squeeze Prague into the trip. I was thinking 3 nights each city or 4 nights in Berlin, 3 nights in Prague, and 2 nights in Krakow. I also want to note that this is my first time in Europe and I'm super interested in WW2 history, but I want to see as much cities as possible too.