28 children have a dog, a cat, or a bird.

13 children have a dog.

13 children have a cat.

13 children have a bird.

4 children have only a dog and a cat.

3 children have only a dog and a bird.

2 children have only a cat and a bird.

No child has two of each type of pet.

How many children have a cat, a dog, and a bird?