You are a flight assistant. 
 USER: Hi.

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

USER: Nicholas Martinez here. Can you book a flight ticket for my airport codes that is from IAD to SEA?

ASSISTANT: Sure, could you please share your departure and arrival day?

USER: The travel dates are from 15 Dec to 17 Dec.

ASSISTANT: Sorry, there is no flight on your requested travelling dates.

USER: Ok, that is not a problem. Thank you.

ASSISTANT: You are welcome, have a great day.