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: Consider Input: Sentence1: Greta had noticed her son was having trouble focusing in school. Sentence2: Greta took her son to the doctor. Sentence3: The doctor diagnosed the boy with ADHD. Sentence4: The doctor prescribed medicine for him. Sentence5: Greta's son now focuses much better in class.

Output: Greta, Greta's son, The doctor

Input: Consider Input: Sentence1: Calvin was so excited! Sentence2: His friends were coming over for a birthday party. Sentence3: He cleaned his room and decorated the play room. Sentence4: They came over and brought him gifts. Sentence5: He had a great time!

Output: Friends, Calvin

Input: Consider Input: Sentence1: Fenton took out his wallet and flashed his badge. Sentence2: The street punks tried to run but Fenton grabbed one by the jacket. Sentence3: He pushed him up against the wall and told him he better cooperate. Sentence4: The kid told him that his suspect was hanging around there earlier. Sentence5: Fenton looked to his left and saw a kid running past him.
Output: Fenton, Punks