Instructions: 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: Donald was visiting his sister in the hospital. Sentence2: His sister was on painkillers. Sentence3: She was sleeping the whole time he was there. Sentence4: Donald needed to go to work. Sentence5: He left without being able to talk to his sister.
Output:
Donald, Sister