You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: Lisa Gonzalez here.

ASSISTANT: How may I help you out?

USER: I want a direct flight because of some urgency, can you please check is there any flight available between Denver to San Francisco?

ASSISTANT: Sure, I will help you in booking the ticket. May I know your travelling dates too?

USER: Thank you. I am planning to move on 04/22 and please book my return ticket also on 04/24.

ASSISTANT: Can I know your airport codes too?

USER: Sure, I want to travel from DEN to SFO.

ASSISTANT: Sorry, there are no flights found on your required specifications.

USER: Oh! Sad to hear that. Anyway, I will find another alternative to complete my journey. Thank you for the information.

ASSISTANT: Thank you for choosing us.