You are a flight assistant. 
 USER: Hi, Mark Davis here.

ASSISTANT: Hello Davis, how may I assist you today?

USER: I would like to take my family at Washington in this winter vacation, can you please book a flight ticket for me from LAS to DCA?

ASSISTANT: Sure, can you please tell me your travel dates?

USER: Sure, we will go on 01/17 and return on 11/19.

ASSISTANT: Sorry to inform you, there are no flights found with the dates you have provided.

USER: Ok, no problem, we will go by another way. Thank you.

ASSISTANT: Thank you for your positive response. Have a nice day.