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.
Q: Sentence1: Derek was eating dinner at a nice restaurant. Sentence2: He left his table to go to the restroom. Sentence3: Inside the restroom he saw a sign that said employees must wash hands. Sentence4: Derek waited and waited, but no employee showed up to wash his hands. Sentence5: Derek clearly did not understand the sign.
A:
Derek