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: I visited my friend Frank in Maine today. Sentence2: He used to own two dogs. Sentence3: I asked him how the dogs were doing. Sentence4: Frank said both dogs got sick and had to be put down recently. Sentence5: I was saddened by this news.
I (myself), Frank, Two dogs