title: Cloud Firestore document read cost for subcollections?
body: <p>How to calculate firestore cost? I know that it count every operation, but if I read one document that contain sub collection how it count? </p>
  
  <p>For example, If I read "A Document" that has 1 "Sub-Collection B" and "Sub-Collection B" have 5 document. Then how much it could if I only read "A Document", it will count 1 or 5 operation? </p>