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: We took the boat out on the lake. Sentence2: Joseph wanted to ski. Sentence3: He grabbed the rope from the back of the boat. Sentence4: He threw it into the water. Sentence5: Then he changed his mind about skiing.
Joseph