Given the task definition, example input & output, solve the new input case.
In this task, you are given a conversation between a flight agent and the customer. You are given 4 options and you need to select the goal of the conversation. It is provided as part of customer's context, which has to be one of the following: `book`: Make a new reservation, `cancel`: Cancel an existing reservation, `no_flight`: No flight found for the customer's preference, `no_reservation`: No reservation / No change / No cancellation was made in the conversation, mostly enquiring details
Example: customer: Hi. 
 agent: Hello. How can I help you? 
 customer: I would like to change my existing reservation as my plan to go for a holiday trip got postponed. Can you please help me with this? 
 agent: Sure, may I know your name please? 
 customer: My name is Anthony Phillips. 
 agent: Please wait a moment. 
 customer: Sure. 
 agent: Unfortunately there is no reservation found with your given name. 
 customer: Not a problem, thank you for checking. 
 agent: Thank you for choosing us.
Output: no_reservation
Here the customer has not asked for any booking, he just wanted to update his already booked flight, so the status would be no_reservation

New input case for you: customer: Hello. 
 agent: Hello, how may I assist you? 
 customer: I need your help to book a flight ticket on 11/18 and 11/20. 
 agent: OK, may I know your origin and destination airport codes? 
 customer: Sure, my origin code is NC-CLT and destination code is CA-SFO. 
 agent: Sorry, unfortunately there is no flight in these travel dates. 
 customer: OK, that's fine. 
 agent: May I know your name please? 
 customer: Sure, I am John Thomas. Thank you. 
 agent: Thank you, have a good day.
Output:
no_flight