Given the task definition and input, reply with output. 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 invited Carl for a beer. Sentence2: They had a nice time. Sentence3: They drank and talk. Sentence4: When they wanted to leave, John found out he had forgotten his wallet. Sentence5: Carl had to pay for a beer.
John, Carl