You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I assist you at this moment?

USER: I'm John Johnson, I am planning to go for DCA from LAS.Can you please help me to book my ticket?

ASSISTANT: Sure, may I know your travelling dates?

USER: My trip dates are 04/16 and 04/18.

ASSISTANT: Sorry John, no flights as per details.

USER: Ok, fine.

ASSISTANT: Thank you for contacting us.

USER: Thank you for giving information.