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: Hello. 
 agent: Hello. 
 customer: Myself Scott Collins. 
 agent: How can I help you? 
 customer: I just want to change my existing reservation Because my seminar was postponed can you help me for that? 
 agent: Unfortunately there is no reservation found under your name. 
 customer: Ok, that's fine. 
 agent: Thank you for reaching us. 
 customer: Thank you for your services. 
 agent: Have a great day.
no_reservation