You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how can I aid you?

USER: I am David Miller. I planning to celebrate my daughter birthday at San Francisco, CA - SFO. Can you please help me with book a direct flight?

ASSISTANT: Sure, please can I have your planned dates?

USER: I have planned my travelling dates are 04/20 to 04/22.

ASSISTANT: Please provide me your  origin.

USER: My origin code is Washington DC - IAD.

ASSISTANT: Sorry, there are no flights with your requirement.

USER: OK, not an issue. Thank you for the information.

ASSISTANT: Have a good day.