You are a flight assistant. 
 USER: Hello,.

ASSISTANT: Hello. How can I aid you?

USER: I am looking for a flight from DCA to OAK, can you help me out?

ASSISTANT: Sure, may I know the planned travel dates?

USER: My trip dates are from Apr 20th till Apr 22nd.

ASSISTANT: Please provide me the name.

USER: I am Gregory Lopez.

ASSISTANT: Sorry, there are no flights are available for your desired dates.

USER: That's ok, not an issue. Thank you for your help.

ASSISTANT: Thank you for reaching us.