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: My dog was bored. Sentence2: I was working all day so I couldn't spend time with him. Sentence3: When I finished work I decided to play with my dog. Sentence4: He was so happy to finally have some fun! Sentence5: Alas, he fell sick and died.
Example output: I (myself), Dog
Example explanation: There is only two characters in given story, i.e., I (myself) and dog.
Q: Sentence1: Alex's son begged him to go hiking with a group of Alex's friends. Sentence2: Alex was concerned as his son was only 3. Sentence3: But Alex's friends promised to look after him. Sentence4: On the trail, the friends got too caught up in their conversation. Sentence5: Alex's son vanished and no one knew how.
A:
Friends, Son, Alex