You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I help you today?

USER: I am Sandra Campbell from Denver. I am planning to meet my school friend in Washington, can you please book a flight ticket within a price limit of 200?

ASSISTANT: Sure, please provide me travelling dates.

USER: I would like to fly on 03/08, return on 03/10.

ASSISTANT: Could you please help me with airport codes?

USER: My source and destination airport codes are CO - DEN, DC - DCA.

ASSISTANT: Please wait while I work on your ticket booking.

USER: Sure.

ASSISTANT: Sorry, we don't have any flight available on given dates.

USER: No problem, thank you.

ASSISTANT: Thank you for checking with us.