Definition: 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.
Input: Sentence1: John bought new headphones. Sentence2: John noticed that the headphones he bought were defective. Sentence3: John returned his defective headphones. Sentence4: With the money he got, John bought a better pair of headphones. Sentence5: John enjoyed his new, functional headphones.
Output:
John