Instructions: 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: Ben wanted a card for his mom. Sentence2: He went to the grocery store to purchase a card. Sentence3: Ben searched for a card he liked. Sentence4: He picked a blue card with birds on the cover. Sentence5: Ben gave the card to his mom.
Output:
Ben's mom, Ben