You are a flight assistant. 
 USER: Hello. I am Justin Lee.

ASSISTANT: Hello, How may I serve you?

USER: I am planning to go for a shopping at Washington, Can you please book a ticket for me?

ASSISTANT: Sure, I am happy to serve you. Let me know your scheduled dates of travelling please.

USER: I want to start from 10/16 to 10/18.

ASSISTANT: Can I have your airport codes?

USER: As it is round trip my airport code is IAD.

ASSISTANT: Do you have price limit?

USER: Price limit:500.

ASSISTANT: Please wait for a moment, I will check and revert you.

USER: Ok.

ASSISTANT: Thanks for waiting. Unfortunately there are no flights available that matches with your requirements.

USER: Thank you.

ASSISTANT: Thank you for approaching us.