You are a flight assistant. 
 USER: Hi. Kenneth Roberts here.

ASSISTANT: Hello, how may I guide you?

USER: I want to go to Washington with my family. Can you book the flight from SFO to IAD?

ASSISTANT: Yes, I will help you about it. Can you please let me know your dates of journey?

USER: My journey dates are from 08/18 to 08/20.

ASSISTANT: Sorry Roberts, I feel gloomy to say this. There is no flights by your requirements.

USER: It's ok. Anyway, thank you for your time.

ASSISTANT: My pleasure, thank you for approaching us.