You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you?

USER: I am Stephen Mitchell here, my planning for a travel is from 10/19 to 10/21 can you please help me to book this ticket?

ASSISTANT: Sure, please tell me your airport codes.

USER: Ok, my airports codes are from OAK to PHL.

ASSISTANT: Sorry Stephen, there are no flights available on your route and date.

USER: Ok, that's fine.

ASSISTANT: Thank you.

USER: You are welcome.