You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello,. May i know your good name?

USER: I am Jerry Collins.

ASSISTANT: How may I assist you?

USER: I want to book a flight ticket with price under 500. Can you help me?

ASSISTANT: sure, can I know your journey dates?

USER: My departure is on 04/05 and return date is on 04/07.

ASSISTANT: May I know your journey codes?

USER: I want to head to DC - DCA from TX - HOU to visit lincoln memorial.

ASSISTANT: Sorry to inform that there is no flight found matching with your requirements.

USER: Ok, no problem. Thanks for your assistance.

ASSISTANT: Thank you.