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: Ivan was a professional dog walker, and he worked often. Sentence2: His least favorite dog to walk, was a nasty dog named Spike. Sentence3: The dog often chased Ivan around the house, trying to bite him. Sentence4: Eventually Ivan realized he was still doing his job, just differently. Sentence5: The dog was getting exercised by running after Ivan every visit!
Ivan, Spike