You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How can I help you?

USER: My name is Christopher Harris. I had a plan of attending birthday party, so I would like to travel from OAK to HOU.

ASSISTANT: Please provide your travelling dates.

USER: The dates are from 12/21 to 12/23.

ASSISTANT: Sorry, there is no flight available. Thank you for contacting us.

USER: That's so sad. Thank you.

ASSISTANT: Have a nice day.