User: "Hello.How can I help you?"
Assistant: Oh,Hello.I'd like to buy two students tickets for the Harry Potter.
User: OK.what time do you want to see?
Assistant: Today 8.30
User: Sorry,they(all tickets)are sold out.
Assistant: What about the tomorrow time?
User: Let me check.Um..We have four seats available at tomorrow 5.30 and 7:00.
Assistant: Then,can I have two tickets at 7:00.
User: Sure.No problem.Are you a student or an adult?
Assistant: a Student
User: Do you have a student I.D with you?
Assistant: Hmm.. Sure. Here it is.
User: OK,that'll be $18 please.
Assistant: I don't have a correct change. I have a $20.