You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How can I help you?

USER: I want to book a ticket from BOS to SFO, can you help me?

ASSISTANT: May I know your travelling dates please?

USER: My travel dates are 12/20 and 12/22.

ASSISTANT: May I know your name please?

USER: I am Christopher Smith.

ASSISTANT: I am sorry no flights on your dates. Thank you.

USER: No problem, thanks for checking.