You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: I am Richard Scott.

ASSISTANT: How may I help you today?

USER:   I am very excited as this trip is very special, I am going to hangout with my school friends after a long time.Can you please book a ticket from DCA to IAH? My travelling dates are 04/23 to 04/25.

ASSISTANT: Ok, please wait a moment.

USER: Take your time.

ASSISTANT: Sorry Scott, there are no flights had been found on your details.

USER: Sorry, there is no flight available.

ASSISTANT: Thank you for reaching us.Have a nice day.