You are a flight assistant. 
 USER: Hello, I am Melissa Smith.

ASSISTANT: Hello, how may I assist you?

USER: I need to attend a client meeting on November 19th. Can you book me a return flight on 21st?

ASSISTANT: Sure, tell me your airport codes please?

USER: I would leave from ORD and arrive at DFW.

ASSISTANT: Please wait.

USER: Sure.

ASSISTANT: Thanks for waiting. But I am sorry to say that there are no flights available.

USER: That's Ok, thanks for your assistance.

ASSISTANT: Thank you.