You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I aid you?

USER: I am Stephen Young. I need to book a flight ticket with direct flight, Can you help me for booking a flight ticket please?

ASSISTANT: Sure, may I know your airport codes?

USER: My source point is CO-DEN to destination point is CA-LAX.

ASSISTANT: Ok, to book a ticket I need your travelling dates.

USER: I would like to start on 01/28 to 01/30. I need price limit with in 200.

ASSISTANT: Please wait for a while.

USER: Sure.

ASSISTANT: Thanks for waiting, there is a no direct flight available with your requirements.

USER: Ok, thanks for your information.

ASSISTANT: Thank you have a nice day.