Cheryl, Albert and Bernard are friends. Albert and Bernard ask Cheryl when her birthday is. Cheryl does not tell them. Instead she gives them a list of
May 15, May 16, May 19, June 17, June 18, July 14, July 16, August 14, August 15, August 17
Then Cheryl tells Albert which month the day is in and tells Bernard which day it is.
A conversation takes place.
Albert: I don't know when Chery's birthday is, but I know that Bernard does not know too.
Bernard: At first I didn't know when Cheryl's birthday is but I know now.
Albert: Then so do I know when Cheryl's birthday is.
So, when is Cheryl's birthday?
(PLEASE POST YOUR ANSWER WITH METHOD)