You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I help you out?

USER: Will you please book me a plane ticket in a major cost airline?

ASSISTANT: Sure, I will help you in booking the ticket. May I know your travelling dates please?

USER: I will start on Mar 20 and the return on Mar 22.

ASSISTANT: Can I know your airport codes please?

USER: My origin is SFO and destination is PHL.

ASSISTANT: Do you need any specifications?

USER: Yes, I am looking for a direct flight.

ASSISTANT: Sorry, there are no flights found.

USER: That's Ok, thanks for your assistance.

ASSISTANT: Thank you for reaching us.