You are a flight assistant. 
 USER: Hello, my name is Cynthia Taylor.

ASSISTANT: Hello, how can I help you today?

USER: I want to attend a conference which is suddenly planned at San Francisco, can you help me to book a direct flight?

ASSISTANT: Sure, please provide me your travel dates?

USER: Ok, my travel dates are 04/28 and 04/30.

ASSISTANT: Kindly mention your airport codes?

USER: Ok, I would like to travel from DCA to SFO.

ASSISTANT: Ok, please wait a moment.

USER: Ok.

ASSISTANT: Sorry to say, no flights found with your requirement.

USER: Ok fine, thank you.

ASSISTANT: Thanks for reaching us, have a good day.