You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello. How may I help you?

USER: Gregory Adams here.

ASSISTANT: Nice to meet you Gregory.

USER: I would like to visit HOU to meet my sister, can you help me to book a flight ticket from DEN?

ASSISTANT: Sure, tell me your travel dates please?

USER: My travelling dates are 27 Oct and 29 Oct.

ASSISTANT: Please wait.

USER: Ok, I will wait for your response.

ASSISTANT: Thanks for waiting. But I am sorry to say that there are no flights available.

USER: Ok, no problem. Thank you for giving information.

ASSISTANT: Thank you.