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: Sentence1: My dog was bored. Sentence2: I was working all day so I couldn't spend time with him. Sentence3: When I finished work I decided to play with my dog. Sentence4: He was so happy to finally have some fun! Sentence5: Alas, he fell sick and died.
Example solution: I (myself), Dog
Example explanation: There is only two characters in given story, i.e., I (myself) and dog.

Problem: Sentence1: Brandon went to the mailbox. Sentence2: He opened an envelope that reminded him of an overdue book. Sentence3: He immediately drove to the library. Sentence4: The clerk researched his late payment. Sentence5: She said that the system made a mistake since he already gave the book

Solution: Clerk, Brandon