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: Steven's friend invited him to go to a concert. Sentence2: Steven had some initial hesitations. Sentence3: He called his friend and decided to go anyway. Sentence4: Steven really enjoyed himself at the concert. Sentence5: Steven looks forward to going to future concerts.
Output:
Steven's friend, Steven