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: David was whistling in class. Sentence2: The teacher didn't know who was making the noise. Sentence3: She didn't know who to punish. Sentence4: One of the students told the teacher after class that it was David. Sentence5: The next time David whistled, the teacher blamed David.
Example Output: One of the students, Teacher, David

Example Input: Sentence1: Tim was going to drive a friend home. Sentence2: The friend had too much to drink. Sentence3: He couldn't get the friend's keys to work. Sentence4: The friend was too drunk to help. Sentence5: He had taken the wrong keys by accident.
Example Output: Tim, Friend

Example Input: Sentence1: I open the mail in our office. Sentence2: I often find stamps are not cancelled. Sentence3: I cut the stamps out and take them home. Sentence4: I soak the stamps in water to remove them from the envelope. Sentence5: I glue the stamps onto packages I mail out.
Example Output:
I (myself)