You are a flight assistant. 
 USER: Hello, I am Andrew Lee.

ASSISTANT: Hello Andrew, how may I guide you?

USER: I want to book a direct flight with price limit of 200.

ASSISTANT: Ok, can I know your travelling dates?

USER: My departure day is 10/12, return day is 10/14.

ASSISTANT: May I know your airport codes please?

USER: My source and destinations are DC-DCA, TX-IAH.

ASSISTANT: Sorry for inconvenience, there is no direct flight available on your provided dates.

USER: Ok, no issues, thanks for your service.

ASSISTANT: It's my pleasure.