Solve the following math problem: Chastity made 12 angel food cakes to give to friends.  She placed the cakes in boxes, and then walked them out to her car.  But she had forgotten her keys.  So, she placed the boxes of cakes in one stack on the hood of her car, and then she ran back into the house to get her keys.  But before she returned, a black crow came, landed on the stack of cakes, and knocked over half of the stack.  When Chastity returned, she picked up half of the fallen cakes, which were not damaged, but the rest of the cakes were destroyed.  How many cakes were destroyed?