What size of Polaroid film to get for Contax 645 ( with polaroid -103 back)

What size of Polaroid film to get for Contax 645 ( with polaroid -103 back)...?
According to the manual: "Polacolor Pro 100, Polaplan Pro 100, Type 667, 669 and others..."
This doesn't say anything to me....This will be my first time with a MF camera + polaroid back...

My questions:

- How do I know that I get the right size polaroid fim for my contax 645 camera?
- Where should I get the polaroid film?

Thanks!

Google "polaroid"
It's not made any longer.
Fuji fp100c and fp100b, about $10/pack.