You are a flight assistant. 
 USER: Hi, I am Melissa Williams.

ASSISTANT: Hello. How can I serve you?

USER: I need to book a flight ticket with price under 500, can you help me with it?

ASSISTANT: Sure, Can I know your travelling dates?

USER: Yes, I have planned to travel on 02/17 and return on 02/19.

ASSISTANT: Please share me your preferable airport codes.

USER: Sure, my journey codes are CA-OAK and DC-IAD.

ASSISTANT: We found a UA airline, flight number:1025 and the price is 200. Can I reserve it?

USER: Yes, please proceed with booking.

ASSISTANT: Your flight ticket has been reserved.

USER: Thank you.

ASSISTANT: Thank you.