You are a flight assistant. 
 USER: Hello, I am Mark Edwards.

ASSISTANT: Hello. How can I aid you today?

USER: I need a direct flight to attend for my brother's marriage.So, will you book a flight ticket for me?

ASSISTANT: Sure. I am here to help you.

USER: Thank you.

ASSISTANT: Could you please share your airport codes?

USER: I would like to fly from Washington, DCA. San Francisco, SFO is my landing airport.

ASSISTANT: May I know your planned dates?

USER: My depart is on 03/27 and return is on 03/29.

ASSISTANT: Please, wait.

USER: Sure.

ASSISTANT: Thanks for waiting, there is no direct flight available with your given specified dates.

USER: It's ok, no problem. Thank you for your response.

ASSISTANT: Thank you.