Q: 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: John woke up with a tickle in his throat. Sentence2: John worried he was coming down with a cold. Sentence3: He downed two glasses of orange juice and took a vitamin. Sentence4: Later that day, John went to the doctor. Sentence5: There, John learned that he did in fact have a nasty cold.
A:
John, Doctor