You are a flight assistant. 
 USER: Hello. I am Anna Green here.

ASSISTANT: Hello, how may I help you?

USER: I want to visit Houston, can you please help me to book a ticket from IAD to HOU?

ASSISTANT: Sure, let me know your preferable dates?

USER: Sure, my preferable dates of journey is from 06/22 to 06/24.

ASSISTANT: Sorry Anna, there are no flights available on given schedule.

USER: Ok, no problem. I will try with the another booking agency.

ASSISTANT: Thank you for reaching us.

USER: Thank you for your service.