You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, how may I help you?

USER: I need you to book a flight ticket from PHL and ORD, please help me.

ASSISTANT: Sure, may I know your trip dates please?

USER: April 12 and 14, are my planned travelling dates.

ASSISTANT: Do you have any other requirements?

USER: I wish to depart in the afternoon and arrives in the evening.

ASSISTANT: Can I know your name please?

USER: My name is Sarah Walker.

ASSISTANT: Ok, please wait. Sorry, we regret to inform you that there is no flight available as per your request.

USER: That's ok, thank you.

ASSISTANT: Most welcome.