Okay, I got a gambling related math/probability problem. Here it is.

If one is using a standard deck of cards and using blackjack valuations (all face cards are 10 but aces are always 1) What would be a proper O/U total for a hold-em flop so the over and under is an even money bet. If you could also provide a proof of it that would be great. My buddies and I at the poker table want another prop to bet on pre-flop.