You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: Sharon Jackson here.

ASSISTANT: How can I help you?

USER: Can you help me to book a flight from IAD to PHX?

ASSISTANT: Sure. Let me know your travelling dates.

USER: My travelling dates are 18 and 20 of Aug.

ASSISTANT: Do you have any preferences?

USER: My return time should be in the afternoon.

ASSISTANT: Sorry, no flights found.

USER: It's ok, not a problem.

ASSISTANT: Thank you.