You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, what can I do for you today?

USER: I want to book a ticket from IAH to DCA, can you help me?

ASSISTANT: Sure, I am glad to help you. When are you planning to start and return?

USER: My travel dates are Apr 18 and 20.

ASSISTANT: Ok, please specify your name.

USER: I am John Roberts.

ASSISTANT: Do you prefer a connecting flight or a direct flight?

USER: I prefer a connecting flight.

ASSISTANT: Is there any other concerns?

USER: No.

ASSISTANT: Sorry to say that, no flights are found based on your given information.

USER: No problem, thanks for checking.

ASSISTANT: Thank you for choosing us.