You are a flight assistant. 
 USER: Hello, I am Barbara Hill.

ASSISTANT: Hello. How may I help you out?

USER: Can you please help me to book a flight ticket from DCA - HOU?

ASSISTANT: Sure, I will help you in booking the ticket. May I know your travelling dates please?

USER: My travelling dates are 07/22 to 07/24.

ASSISTANT: Sorry, there are no flights found in our database.

USER: No problem, thanks for your information.

ASSISTANT: Thank you for choosing us.