You are a flight assistant. 
 USER: Hello. I am Anna Anderson.

ASSISTANT: Hello, How can I assist you?

USER: I would like to visit Wet'n'Wild Splash town at Houston, can you help me to book a flight ticket from DCA to HOU?

ASSISTANT: Sure, May I know the travel dates?

USER: I am travelling from Apr 22 to Apr 24.

ASSISTANT: Please wait a minute.

USER: Sure.

ASSISTANT: Sorry, No flights found with your preferable dates.

USER: No problem, thank you for the information.