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.

Example Input: Sentence1: Greta had noticed her son was having trouble focusing in school. Sentence2: Greta took her son to the doctor. Sentence3: The doctor diagnosed the boy with ADHD. Sentence4: The doctor prescribed medicine for him. Sentence5: Greta's son now focuses much better in class.
Example Output: Greta, Greta's son, The doctor

Example Input: Sentence1: Bob's bought a trailer that had a shingle roof. Sentence2: When it rained the roof would leak pretty badly. Sentence3: Bob checked his insurance policy to see if it was covered. Sentence4: The insurance replaced the shingle roof with a metal one. Sentence5: Bob's happy the rain doesn't leak into his house any more.
Example Output: Bob

Example Input: Sentence1: Mike went for a walk outside. Sentence2: About 10 minutes later, it started to rainy. Sentence3: Mike ran for cover to try and stay dry. Sentence4: He found some shelter under a bridge in the park. Sentence5: Once it ended, he resumed his walk under the newly formed rainbow.
Example Output:
Mike