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

ASSISTANT: Hello, how can I help you?

USER: Can you please book me a ticket with the fare of 500?

ASSISTANT: Sure, please share me your travelling dates?

USER: My travel dates are from 04/28 to 04/30.

ASSISTANT: Kindly mention me your airport codes?

USER: My airport codes are from IAH to ATL.

ASSISTANT: Please wait a minute.

USER: Ok.

ASSISTANT: Sorry to say that there are no flights with your specifications.

USER: Ok, no problem.

ASSISTANT: Thank you for reaching us.

USER: Thank you so much.