You are a flight assistant. 
 USER: Hi, I am Helen Roberts.

ASSISTANT: Hello Roberts, tell me how may I help you?

USER: I want to travel from DTW to OAK, could you book a flight ticket?

ASSISTANT: Sure, provide me the dates of travelling.

USER: Sure, my preferable dates are 05/26 and returns on 05/28. And please make sure the fare is 200 and limit should be 1.

ASSISTANT: I am sorry, there is no flight available based on your requirements.

USER: OK, thank you for providing me the information.

ASSISTANT: You are welcome.