You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How may I help you?

USER: I am Patricia Johnson want to visit Las Vegas, can you help me to book a direct flight?

ASSISTANT: Sure, tell me your travel dates please?

USER: Sure, my travelling dates will be 01/08 and 01/10.

ASSISTANT: Ok, now please tell me your airport codes?

USER: Yes, I want to fly from DEN to LAS.

ASSISTANT: Thanks for your time and patience. But I am sorry to say that presently there are no flights available.

USER: That's ok, thank you.

ASSISTANT: Thank you.