You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: I am Helen Miller here.

ASSISTANT: Miller, how may I guide you?

USER: I want to reserve my ticket from IAD to LAS, can you please help me to book a ticket?

ASSISTANT: Sure, I am here to help you. When would you like to travel?

USER: Sure, my willing to travel dates are from 05/15 to 05/17.

ASSISTANT: Just a moment.

USER: Sure.

ASSISTANT: Miller, sorry to inform that no flights are available on your prefer dates.

USER: Ok, no problem. Anyways, thank you for your service.

ASSISTANT: You are most welcome, thank you Miller for contacting us.