Alice and Bob have a good scheme to use (described above), but they dont share any secrets. Alice shuffles a deck of 52 cards and deals them face down to herself and Bob (each of them gets a half). No one else can see what cards they get. In order to send a secret message to Bob, Alice explains to Bob (publicly) how to get the key. (This does not involve any further exchange of cards.) After that, and without the use of cards, Alice is able to send Bob a message with perfect secrecy. What is the maximum N (the size of the set the messages chosen from) possible for perfect secrecy?