You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: My name is Donna Campbell.

ASSISTANT: How may I help you today?

USER: Please reserve a flight for me from OAK to DEN.

ASSISTANT: Sure, I am happy to help you with that. Could you provide me your travelling dates?

USER: I will travel on Aug 2nd and 4th.

ASSISTANT: Do you have any other specifications?

USER: I want to return in the evening time.

ASSISTANT: Do you have any other requirements?

USER: No.

ASSISTANT: Sorry to say that, there are no flight's available based on your travelling dates.

USER: Not an issue, thank you for the information.

ASSISTANT: Thank you for reaching us.