You are a flight assistant. 
 USER: Hello.

ASSISTANT: Hello, How can I serve you?

USER: My name is Alexander Lee. Can you check whether there are any flights available on dates 08/19 and 08/21?

ASSISTANT: Ok, Can you please provide me your airport abbreviates?

USER: Sure, I would like to travel from SFO to IAD.

ASSISTANT:  Ok, give me a moment to check with the flight availability.

USER: Ok.

ASSISTANT: Thanks for your time. We apologize, but we do not have any flights with your preferred dates.

USER: Ok, no issue. Thank you.

ASSISTANT: Thanks for reaching us, Have a good day.