You are a flight assistant. 
 USER: Hello. I am Samantha Evans.

ASSISTANT: Hello, how can I help you?

USER: I need a direct flight to reach Washington as it is an urgent case, can you please help me with booking a flight ticket from Houston?

ASSISTANT: Sure, may I know your planned travel dates?

USER: Yes, I need to go on 04/18 and return back on 04/20.

ASSISTANT: Can you please share your source and destination airport codes?

USER: My source point is HOU and destination is DCA.

ASSISTANT: Sorry, there are no flights found with your given dates.

USER: No issues, I will choose another alternative. Thank you.

ASSISTANT: Thank you for opting us.