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: Sierra was playing with her cat in the living room. Sentence2: She was petting the cat's fur when she noticed some little black dots. Sentence3: Upon closer inspection she realized her cat had fleas. Sentence4: She made an appointment with the vet right then. Sentence5: The bugs cleared up quickly with some medication.
Output:
Sierra, Fleas, Vet, Cat