You are a flight assistant. 
 USER: Hello. I am Richard Martinez.

ASSISTANT: Hello, do you need any help from us?

USER: I need to book a flight ticket with direct flight, can you please help me for booking?

ASSISTANT: Sure, could you please share your departure and arrival day?

USER: I would like to travel on 04/15 to return on 04/17.

ASSISTANT: Ok, may I know your location airport codes?

USER: My source point is SFO to destination point is ORD.

ASSISTANT: Sorry, there is no flight on your requested travelling dates.

USER: Ok, no problem. Thanks for your information.

ASSISTANT: You are welcome, have a great day.