You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: I am David Lewis here.

ASSISTANT: How may I assist you?

USER: I want to reserve my ticket from LAX to SFO to visit San Francisco, can you please help me?

ASSISTANT: Sure, may I know your planned travel dates please?

USER: Sure, my preferable dates of journey are from Sep, 21 to Sep, 23.

ASSISTANT: Do you have any specifications?

USER: Yes, I need a price limit of 200.

ASSISTANT: David Lewis, no flights has been found on your planned travel dates.

USER: Ok, that's fine. Anyways, thank you for your service.

ASSISTANT: Thank you for approaching us.