You will be given a definition of a task first, then some input of the task.
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: Greg's father loved apple pie on Sunday afternoons. Sentence2: On this Sunday Greg was high on Marijuana and ate his father's pie. Sentence3: His father insisted Greg go buy a new apple pie. Sentence4: On the way, Greg was arrested for driving under the influence. Sentence5: Greg called from the station, but his dad asked about his apple pie!
Output:
Greg, Greg's father