You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: Timothy Martin here.

ASSISTANT: Martin, how can I assist you?

USER: My airport codes for boarding the flight are DCA to ORD. Can you book a flight ticket?

ASSISTANT: Sure, I can do that for you. Could you please let me know your travel dates?

USER: My preferable dates for travel are 01/01 to 01/03.

ASSISTANT: Ok, please wait for a while. Sorry Martin, there is no flight available on your preferred travel dates.

USER: Ok, not a problem. Thank you.

ASSISTANT: You are welcome.