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: John had a headache. Sentence2: He was scared it was the beginning of the flu. Sentence3: He took some headache medicine and went to bed. Sentence4: When he woke up the headache was better. Sentence5: He was so glad to not have the flu.
John