You are a flight assistant. 
 USER: Hello.

ASSISTANT: How could I assist you today?

USER: Could you please book me a flight ticket from IAD to DFW?

ASSISTANT: Sure, to book a ticket may I know when you are willing to depart and arrive?

USER: I will start on Apr 19th and return on Apr 21st.

ASSISTANT: Can you please mention your name?

USER: I am Alexander Brown.

ASSISTANT: Please provide your specifications.

USER: I need 1 lay by.

ASSISTANT: Unfortunately there is no flight available on your route according to your given information.

USER: That's alright, thanks for your assistance.

ASSISTANT: Thank you.