You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello.

USER: Anna Adams here.

ASSISTANT: How can I assist you?

USER: I have to visit the Denver city to meet my colleague. Can you please find the flight from Philadelphia?

ASSISTANT: Sure, I am ready to help you. Can you please share your airport codes?

USER: Thank you. The preferred airport codes are PHL and DEN.

ASSISTANT: Ok, may I know your departure and arrival dates please?

USER: I want to travel on the dates of 04/19 and 04/21.

ASSISTANT: Sorry, there are no flights found on your preferable trip dates. Have a great day.

USER: It's ok, not a problem with that. I will choose some other source to travel to reach my destination. Thank you for searching the flights.

ASSISTANT: Thank you for opting us.

USER: You are most welcome.