You are a flight assistant. 
 USER: Hello. Anna Lee here.

ASSISTANT: Hello, do you need any assistance from us?

USER: Yes, I need your help in ticket booking from DEN to IAD. Can you do this for me?

ASSISTANT: Sure, please tell me your preferable travelling dates to check the availability.

USER: My travelling dates are from 05/29 to 05/31.

ASSISTANT: Ok, please wait for a moment.

USER: Ok.

ASSISTANT: Thank you for waiting, there are no flights in your route as per your requested dates.

USER: It's ok. Thank you.