How to count the number of cells before a condition is met?

Hi guys,

I have a nice little problem that I cannot seem to get my head around. Say I have sales data of a product that doesn't sell every day. For instance, in Column A of the attachment, you will find some rows with a positive number but many rows with zeros. In the attachment, I let each row represent a separate date (with the same time interval per row).

I would like to add a column describing the number of rows it takes to get to the previous sales day with non-zero sales. But I have no clue which formula to use for it. I could use a progressive series of IF statements but this is ugly.
I have hardcoded the desired result in column B, labeled "intervals".

Any help is much appreciated!
Thanks,
Stuart