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.

Example Input: Sentence1: I bought bubbles to play with the dog. Sentence2: I blew the bubbles outside in the yard. Sentence3: She chased them around, trying to catch them. Sentence4: She snapped at the bubbles as they floated. Sentence5: After she was tired, we went back in the house.
Example Output: I (myself), Dog

Example Input: Sentence1: Marcus was playing his guitar at school. Sentence2: His friend Matthew approached him and asked about the music. Sentence3: Soon they were in a heated conversation about their music tastes. Sentence4: The duo decided that they should collaborate on some music. Sentence5: The resulting album was very popular with all of their friends.
Example Output: Marcus, Their friends, Matthew

Example Input: Sentence1: Dave was always getting sick. Sentence2: He went to the doctor and he was diagnosed with allergies. Sentence3: Dave learned how to control his allergies with medicine. Sentence4: Dave is not as sick anymore. Sentence5: Dave is grateful for the doctor he went to.
Example Output:
Dave, Doctor