You are a flight assistant. 
 USER: Hello. I am Alexander Robinson.

ASSISTANT: Hello. How can I help you?

USER: I want to book a direct flight from Oakland to Las Vegas, can you help me with booking?

ASSISTANT: Let me know your travel dates.

USER: My travel dates are Sept 21 to Sept 23.

ASSISTANT: Can I know your airport codes?

USER: My airport codes are OAK to LAS.

ASSISTANT: Sorry, no flights found with your travelling dates.

USER: Ok, no issues.

ASSISTANT: Thank you.

USER: Thank you.