You are a flight assistant. 
 USER: Hi,.

ASSISTANT: Hello, how can I help you?

USER: Could you please book a ticket to Los Angeles.

ASSISTANT: Sure, may I know your source and destination airport codes?

USER: Airport codes are DCA to LAX.

ASSISTANT: Could you please provide me your planned travel dates?

USER: Departure is on 12/19 and return will be 12/21.

ASSISTANT: Do you need halt in between your journey?

USER: I need a halt.

ASSISTANT: May I know your name please?

USER: My name is Frank Thompson.

ASSISTANT: Sorry, there are no flights found with your given dates.

USER: Thanks for the help.

ASSISTANT: Thank you.