Detailed Instructions: 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.
Problem:Sentence1: Greg is an old man. Sentence2: He stays active by walking. Sentence3: One day he decided to walk by an unfamiliar road. Sentence4: During this walk he tripped over a crack in the road. Sentence5: Greg hurt himself badly, but decided not to see a doctor.
Solution:
Greg, Doctor