Given the task definition and input, reply with output. 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: Dave was always getting sick. Sentence2: He went to the doctor and he was diagnosed with allergies. Sentence3: Dave learned how to control his allergies with medicine. Sentence4: Dave is not as sick anymore. Sentence5: Dave is grateful for the doctor he went to.

Dave, Doctor