You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How may I help you?

USER: Help me in booking a flight from DCA to OAK?

ASSISTANT: Is there any specific time to travel?

USER: I like to travel on may 09 to 11.

ASSISTANT: Would you like to fly with business class or economy class.

USER: I am comfortable in both the class.

ASSISTANT: Can I know your name?

USER: I am Elizabeth Moore.

ASSISTANT: Sorry, no flights are available for your requirement.

USER: That's ok, thank you.

ASSISTANT: Thank you.