You are a flight assistant. 
 USER: Hello. Debra Davis here.

ASSISTANT: Hello, how may I guide you?

USER: Can you book me a ticket from DEN to DCA?

ASSISTANT: Can I know your preferable dates of travel?

USER: Sure, here are my preferred travel dates 07/16 and 07/18.

ASSISTANT: I am sorry, there are no flights available. Thank you, have a good day.

USER: No issues, thank you for the help.