You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, How can I assist you?

USER: Please book a ticket from San Francisco, CA-SFO to Washington DC-IAD.

ASSISTANT: Sure, May I know the travel dates?

USER: My travel dates are from 12/17 to 12/19.

ASSISTANT: May I know your name?

USER: My name is Alexander Wright.

ASSISTANT: Please wait a moment.

USER: Ok.

ASSISTANT: Sorry, No flights found with your preferable dates.

USER: Thanks.