Formula to count days since last accident

I have a list of dates in Column A, and either "Yes" or "No" in Column B, indicating whether or not there was a work-related accident on that day. Every day, a Yes or No is placed into Column B, next to that day's date.

Example:

01/04/2012 No
01/05/2012 Yes
01/06/2012 No
01/07/2012 Yes
01/07/2012 No
01/09/2012 No
01/10/2012 No
01/11/2012 No
01/12/2012 No
01/13/2012 No
01/14/2012
01/15/2012
01/16/2012

I am trying to create a formula that counts the number of "No's" under the last "Yes"... So in the above example, the result of the formula would be a 6. I.E. "There have been 6 days without a work-related accident." And as soon as a "Yes" is entered, the count goes back to zero. If I were to replace the last "Yes" in my example above with a "No" - the result of the formula would be 8.

I'm trying to do this without utilizing VBA or custom functions... Only with the built-in excel functions. Thanks in advance for any assistance!