Four times a week, but since mondays only include shoulder movements and calves (For what I have a very good reason - so don't you go all laughs at me), you could take it down to three core days ..
Since i'm at school i go w/ my available time. Sometimes it's 2-3 times a week, and other times i'll go 4-5 days/week. It's always good to mix things up every now and then as well, so i just go w/ the flow, b/c whether i like it or not it's a mandatory switch of days going to gym.