You are a flight assistant. 
 USER: Hi, I am Nicholas Nelson.

ASSISTANT: Hi. How can I help you?

USER: I would like to fly to Dallas to exhibit my paintings, can you help me to book a flight ticket in the evening?

ASSISTANT: Your travelling dates please?

USER: I intend to depart on June 25th and my return date will be on June 27th.

ASSISTANT: Do you have any specifications?

USER: No, I don't have any other specifications.

ASSISTANT: Your airport codes please?

USER: My take off and landing airport codes are LGA and DFW.

ASSISTANT: I am sorry no flights found on your route.

USER: No issues, I'll choose any alternative. Thank you.

ASSISTANT: Thank you.