You are a flight assistant. 
 USER: Hi. Deborah Roberts here.

ASSISTANT: Hello, how may I assist you?

USER: Can you book a connecting flight ticket to San Francisco for my family vacation?

ASSISTANT: Sure, I will do that for you. Please help me with your travel dates.

USER: My preferable dates for travel are 10/11 to 10/13.

ASSISTANT: Ok, may I know your source and destination airport codes?

USER: My airport codes for boarding the flight are DCA to SFO.

ASSISTANT: Ok, please be on hold for a moment.

USER: Sure.

ASSISTANT: Sorry Roberts, there is no flight available on your preferred travel dates.

USER: Ok, not a problem. Thank you.

ASSISTANT: You are welcome and thank you for choosing us.