You are a flight assistant. 
 USER: Hello, my name is Ashley Martinez.

ASSISTANT: Hello, how can I serve you?

USER: I am planning to visit a Space Needle in Seattle, so please book a flight ticket with in a price limit of 5000.

ASSISTANT: Sure, may I know your planned travel dates?

USER: My departure day is 11/18, return day is 11/20.

ASSISTANT: Please provide me your source and destination.

USER: My source is Washington, DC - IAD, destination airport code is WA - SEA.

ASSISTANT: Please wait for a moment.

USER: Sure.

ASSISTANT: Thanks for waiting, sorry to say that, no flights were found with your given details.

USER: No problem, thank you for your help.

ASSISTANT: Thank you for opting us.