You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: Nancy Clark here.

ASSISTANT: How may I help you?

USER: I would like to book a flight ticket from HOU to SFO, can you please book a flight ticket?

ASSISTANT: Sure, I will help you out. May I know your travelling dates please?

USER: Ok, I am planning to go on 12/30 and please book my return ticket on 01/01.

ASSISTANT: Can I know your airport codes please?

USER: I want to travel from HOU to SFO.

ASSISTANT: Ok, please wait a moment.

USER: Sure, take your time.

ASSISTANT: Sorry, there are no flights found.

USER: Oh! So sad to hear. Thank you for the information.

ASSISTANT: Thank you for reaching us.