You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: I am David Jackson here.

ASSISTANT: How can I aid you today?

USER: I want to reserve my ticket from BOS to DEN, can you please help me in booking my ticket?

ASSISTANT: Sure, I am here to help you. May I know your travel dates please?

USER: Sure, my planned dates of journey are from Jan, 25 to Jan, 27.

ASSISTANT: Ok, do you have any specifications?

USER: Yes, I need a return time at evening.

ASSISTANT: Ok, hold on for a moment. Let me check the best available flight for you.

USER: Sure, I will wait.

ASSISTANT: Sorry David Jackson, there are no flights available on your requested dates.

USER: Ok, no problem. Anyways, thank you for your service.

ASSISTANT: Welcome, thank you for choosing us. Have a great day.