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.

Example Input: Sentence1: John did not know how to roller skate. Sentence2: His friend said that he would teach him. Sentence3: They spent all day practicing skating. Sentence4: John kept trying and got very good. Sentence5: Now he roller skates all over the neighborhood.
Example Output: John, Friend

Example Input: Sentence1: Bob loved to eat fat. Sentence2: His friends thought he ate too much. Sentence3: Indeed, the fat increased Bob's cholesterol intake dramatically. Sentence4: Bob's arteries were becoming clogged. Sentence5: After many years, Bob had a heart attack and died.
Example Output: Friends, Bob

Example Input: Sentence1: The girls went to the shopping mall. Sentence2: They wanted to hang out together for a little while. Sentence3: Three boys approached the girls and started talking to them. Sentence4: They all ended up getting lunch together in the food court. Sentence5: Afterwards everyone walked the mall together.
Example Output:
Boys, Girls