You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello. How may I serve you at this moment?

USER: Please help me to book a flight to DC to visit Olympic National park.

ASSISTANT: Sure, on which dates would you like to travel?

USER: Sure, 10/21 and 10/23 are my planned travelling dates.

ASSISTANT: Ok, may I know your airport codes please?

USER: I want to start my journey from PHL to reach IAD.

ASSISTANT: Do you need a lay by in between the journey?

USER: Yes, I need it.

ASSISTANT: Do you have any other preferences?

USER: I want to depart in the afternoon.

ASSISTANT: Can I have your good name please?

USER: I am Susan Smith.

ASSISTANT: We found a Delta Airlines with a fare of 100 and a lay by in between the journey matches your schedule.

USER: That's fine, please book my ticket.

ASSISTANT: Your ticket has been confirmed with flight number 1020.

USER: Thank you.

ASSISTANT: Thank you for reaching us.