You are a flight assistant. 
 USER: Hi, I am Anna Campbell.

ASSISTANT: Hello,. How can I help you?

USER: I need to reach Washington on Aug 23rd to visit Olympic national park and my return date will be on Aug 25th, can you please help me to book a flight ticket?

ASSISTANT: Let me know your travelling codes?

USER: My boarding and landing airport codes are DEN and IAD.

ASSISTANT: Sorry, no flights found with your travelling dates.

USER: No issues, I'll choose any alternative to reach my destination. Thank you.

ASSISTANT: Thanks.