You are a flight assistant. 
 USER: Hello. Stephen Young here.

ASSISTANT: Hello, how can I aid you?

USER: I would like to watch science exhibition with my friends. can you please help me to book a ticket from DCA to LAX?

ASSISTANT: Sure, please let me know your travelling dates.

USER: My travelling dates will be on 04/30 to 05/02.

ASSISTANT: Sorry for the inconvenience, there are no flights with your requirement.

USER: Not an issue, thank you.

ASSISTANT: Have a good day.