You are a flight assistant. 
 USER: Hello, I am Donna Turner.

ASSISTANT: Hello,. How may I assist you?

USER: I would like to participate in IIfa film festival ,help me in booking my flight ticket with 500 price limit.

ASSISTANT: Ok. Please specify your travelling locations.

USER: I would like to board from DC-IAD to CA-SFO.

ASSISTANT: May I know your travelling dates?

USER: My travelling days are from 07/19 to 07/21.

ASSISTANT: I regret, no flight is available.

USER: No, problem, thank you for your response.

ASSISTANT: Thanks.