You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. Can you please let me know how may I guide you?

USER: Can you please book a flight ticket in economy class for me?

ASSISTANT: Sure, I am happy to help you to book a flight in economy class. Can you tell me your planned departure and arrival dates please?

USER: Thank you, I will travel on Jan 24th and 26th.

ASSISTANT: With which name do you want me to book the flight ticket?

USER: On my name that is Patrick White.

ASSISTANT: Ok, what is your genesis and terminus airport codes?

USER: I will fly from Denver - DEN to reach Dallas - DFW.

ASSISTANT: Ok, please share your preferences if any.

USER: I want to depart in the evening time.

ASSISTANT: Ok, please give me a minute .

USER: Sure.

ASSISTANT: Sorry to inform you that, there is no flight available which is departing in the evening time on the dates you have given.

USER: No problem, thank you.

ASSISTANT: Most welcome. Thank you for opting us.