You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I help you?

USER: Can you please help me to book a flight ticket from SFO to DCA?

ASSISTANT: Sure, let me know your trip dates please?

USER: Thank you. My planned trip dates are Sept 9th and 11th.

ASSISTANT: May I know your connection limit?

USER: I need a direct flight in a normal-cost airlines.

ASSISTANT: Do you need any other preference?

USER: I am looking for a flight which is returning in the evening time. I prefer to travel in an economy class flight.

ASSISTANT: Can I know your name please?

USER: My name is Stephanie Carter.

ASSISTANT: Sorry to inform you that there are no flight services available on your given details.

USER: It's ok, not a problem with that. Thank you for your help.

ASSISTANT: Thanks for contacting us.

USER: You are welcome.