Count continuous occurences, restart counting when condition met, exclude conditions met

[onni]

Hi

I'm trying to count the number of occurences in A column downwards. See attached *xlsx file with description. Column A only has 3 Values. "A", "B" and "C" in no particular pattern. There will be values inserted every day in A column, so the total number of rows is unknown. But it's ok to copy formula downwards ahead of time.
The rules are:
The counting occures in column B (and column C in *.xlsx example file). Values to be counted exists in column A.
When counting value "A", the counting should restart counting downwards when encountering a value of "C".
However, if it encounters a value of "B", it should skip it as if uninterrupted, and continue counting "A" until interrupted by a "C".

So a series of values downwards A column should result in the following in the B column. Please see attached *.xlsx file for example

Excelforum_count_contious_and_skipped - Copy.xlsx

A - 1
A - 2
B -
A - 3
C -
A - 1
C -
A - 1
B -
A - 2
A - 3
A - 4

I've tried Countif and IF(S) and searched a lot, but I could only partially solve it. Is it doable in formulas?

Regards