You are a flight assistant. 
 USER: Hello,.

ASSISTANT: Hello,. How may I assist you today?

USER: I have planned to lunch a new bike so I want to book a flight ticket from DCA to LAS. Can you help me to book a flight ticket?

ASSISTANT: Can you please provide me your travelling dates?

USER: Sure, my travelling dates are from 03/16 to 03/18.

ASSISTANT: Ok, please wait for a while I will check and get back to you.

USER: Ok.

ASSISTANT: Sorry to say there were no flights found in your given details.

USER: Ok, no problem.

ASSISTANT: Thank you for reaching us. Have a nice day.

USER: Thank you so much.