You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I help you?

USER: I'm Steven Baker. Can you help me to book a ticket from CA - SFO to TX - DFW?

ASSISTANT: Sure, please provide your travelling dates.

USER: Yes, my travel dates are 12/20 and 12/22.

ASSISTANT: Please give me a moment.

USER: OK.

ASSISTANT: Thanks for waiting Steven. Sorry to say that unfortunately there is no flights found under your requirement.

USER: OK, thank you.

ASSISTANT: Thanks for reaching us. Have a nice day.