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.

Ex Input:
Sentence1: Ken was a cook. Sentence2: Ken was given an order for a medium rare steak. Sentence3: Ken cooked up the steak nice and rare. Sentence4: He went to serve it to the customers. Sentence5: The customer told him they wanted it well done.

Ex Output:
Customer, Ken, Customers

Ex Input:
Sentence1: Bob's bought a trailer that had a shingle roof. Sentence2: When it rained the roof would leak pretty badly. Sentence3: Bob checked his insurance policy to see if it was covered. Sentence4: The insurance replaced the shingle roof with a metal one. Sentence5: Bob's happy the rain doesn't leak into his house any more.

Ex Output:
Bob

Ex Input:
Sentence1: David went to china with his girlfriend. Sentence2: They went to beijing first. Sentence3: They tried to climb the great wall. Sentence4: David's girlfriend wanted to stop after 20 minutes in. Sentence5: They ended up leaving.

Ex Output:
Girlfriend, David