In this task, you're given a story (which contains five sentences only). Your task is to find all the characters which are available in the given story.

Sentence1: John spent hours writing his English essay that was due the next day. Sentence2: After dinner he went back to his room to finish it. Sentence3: He found a pile of wet and shredded paper on the floor near his dog. Sentence4: John had to tell his teacher that the dog ate his homework. Sentence5: John was usually a very good student so his teacher believed him.
John, Dog, Teacher