Given the task definition and input, reply with output. 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.

Sentence1: Yesterday someone knocked at my door. Sentence2: It was a person trying to sell knives. Sentence3: He wanted to demonstrate them to me. Sentence4: I was obviously uncomfortable letting in a stranger with knives. Sentence5: He continued to try as I shut the door.
I (myself), Someone