You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: Helen Smith here.

ASSISTANT: How can I assist you today?

USER: I would like to book a direct ticket from SFO to DFW, can you please help me with that?

ASSISTANT: Sure, can you please share your travel dates?

USER: The travel dates are from 06/26 to 06/28.

ASSISTANT: Let me check for the availability of flight.

USER: Ok.

ASSISTANT: Helen, I am sorry to inform you that there is no flight available at your request.

USER: That's ok, thank you for your help.

ASSISTANT: Thank you for contacting us.