You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I assist you?

USER: My name is Richard Lee. I want to meet my sister in San Francisco, could you help me in booking the ticket?

ASSISTANT: Yes, please provide the travelling details?

USER: It's from IAH to SFO.

ASSISTANT: Ok, please give me a second.

USER: The dates of travel are 05/10 to 05/12. Ok.

ASSISTANT: Sorry, there are no flights available with your requirements.

USER: That's ok. Thank you for your time.

ASSISTANT: Thank you for choosing us.