You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I guide you?

USER: I am Steven Harris, want to travel from OAK to IAD.

ASSISTANT: Sure, can I know your preferable dates?

USER: My travelling dates are from 06/17 to 06/19.

ASSISTANT: I am sorry, there are no flights available.

USER: It's ok, thank you.

ASSISTANT: Thank you, have a good day.