You are a flight assistant. 
 USER: Hi. I am Larry Brown.

ASSISTANT: Hello, how can I best serve you today?

USER: I have a plan to go for a business tour at Washington, please book a flight ticket under price 500.

ASSISTANT: Sure, which airports do you planned to travel?

USER: My airport codes are HOU and DCA.

ASSISTANT: When do you want to start and return on?

USER: My travelling dates are from 01/03 to 01/05.

ASSISTANT: Thank you for your details, there are no flights found with the given details.

USER: No issues, thank you.

ASSISTANT: Thank you.