You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: Helen Roberts here.

ASSISTANT: How may I serve you?

USER: I want to attend a Seminar in Washington. Can you please help me for booking the flight ticket?

ASSISTANT: Sure, I will help you in flight ticket booking.

USER: Thanks.

ASSISTANT: Ok, now please share your travel dates?

USER: My travelling dates are from 06/25 to 06/27.

ASSISTANT: Sure, may I know your airport codes please?

USER: My airport codes are from BOS to IAD.

ASSISTANT: Thanks for waiting patiently.

USER: My pleasure.

ASSISTANT: But I am sorry to say that there are no flights available.

USER: Anyway, thanks for the information.

ASSISTANT: Thank you.