You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How can I assist you today?

USER: I am Patrick Mitchell. I am planning to visit a NASA space center in Houston, so please book a flight ticket on Feb 24.

ASSISTANT: Sure, can you please share your travel dates?

USER: I want to fly on Feb 24, return on Feb 26.

ASSISTANT: Could you please help me with the airport codes?

USER: My source and destination airport codes are OAK and IAH.

ASSISTANT: Do you have any class preference?

USER: No.

ASSISTANT: Patrick Mitchell, I am sorry to inform you that there is no flight available at your request.

USER: Ok, no problem. Thank you.

ASSISTANT: You are welcome. Thank you for contacting us.