Definition: 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: Sentence1: Thorn was rowing his boat on a lake. Sentence2: He dipped his pole into the water. Sentence3: He felt a tug on his hook. Sentence4: He pulled up a large sturgeon. Sentence5: Thorn felt bad and let the fish back into the water.
Output:
Thorn, Fish