You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how can I help you?

USER: I am Andrew King. I want to visit. Philadelphia for a meeting. Please book a flight ticket under price 500.

ASSISTANT: Sure, please share me your travelling dates?

USER: My travelling dates are from 01/16 to 01/18.

ASSISTANT: Kindly assign me your airport codes?

USER: My airport codes are Source code is HOU and Destination code is PHL.

ASSISTANT: Please wait a minute.

USER: Ok.

ASSISTANT: Sorry, there were no flights with your specifications.

USER: That's fine, thanks for the information.

ASSISTANT: Thank you for reaching us.