Teacher: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
Teacher: Now, understand the problem? Solve this instance: customer: Hello. 
 agent: Hello, how may I help you? 
 customer: I want to change my existing reservation, due to some personal work. Can you please help me with this? 
 agent: Sure, please wait for a while. 
 customer: Sure, I am Richard Hill. 
 agent:  Sorry, no active reservation found on your name in our data base. 
 customer: Ok, Thank you for your service. 
 agent: Welcome, thank you for reaching us.
Student:
no_reservation