Given the task definition and input, reply with output. 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

customer: Hi. 
 agent: Hello. 
 customer: I am Charles Miller. 
 agent: How may I help you out? 
 customer: I want to cancel my reservation, can you help in that? 
 agent: Sure, I will help you in cancelling the reservation. 
 customer: Sure. 
 agent: Sorry, there are no reservations found in our database. 
 customer: That's ok, thank you for your help. 
 agent: Thank you for choosing us.
no_reservation