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: John was at work. Sentence2: He turned on the light but nothing happened. Sentence3: He flicked the switch a few times. Sentence4: After three times the light turned on. Sentence5: John put in a work order to have the light switch replaced at work.
John