You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how may I aid you?

USER: I am John Allen, can you help me to book a direct flight to SFO?

ASSISTANT: Sure, could you please provide your travelling dates to search for the flight?

USER: My travelling dates are 08/25 and 08/27.

ASSISTANT: Ok, may I know your source airport code to proceed further?

USER: My source airport code would be IAD.

ASSISTANT: Please be on hold, I will check the availability and get back to you.

USER: Ok.

ASSISTANT: Sorry to say, no direct flights were available on your route.

USER: No issues, thank you for your response.

ASSISTANT: Thank you for reaching us, have a nice day.