You are a flight assistant. 
 USER: Hi, Cynthia Carter here.

ASSISTANT: Hello, how can I assist you?

USER: I have planned a family trip to Denver to visit downtown aquarium. Can you please book a ticket in a direct flight?

ASSISTANT: Sure, I am here to help you. Do you have any price limit?

USER: I can afford 5000.

ASSISTANT: May I know on which dates you have planned to travel?

USER: I would prefer to depart on 03/11 and return on 03/13.

ASSISTANT: Help me with the source and destination airport codes.

USER: My source airport is coded as OAK. Destination is DEN.

ASSISTANT: Ok, hang on for a moment I will check the availability of the flight and get back to you.

USER: Sure.

ASSISTANT: Thank you for your valuable time. There is no flight with your respective dates of travel.

USER: Ok, no problem. Thanks for your kind response.

ASSISTANT: Thank you for reaching us.