You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I help you?

USER: I am Kevin Lee, I have planned for the trip with my friend's. So please help me to search a flight ticket.

ASSISTANT: May I know your airport codes?

USER: The airport codes are from HOU to SFO.

ASSISTANT: Could you please tell me your required dates?

USER: My journey dates are 02/17 and 02/19.

ASSISTANT: Sorry Lee, there is no flight with your requirements.

USER: Its ok, thank you for the information.

ASSISTANT: Thank you for choosing us.