How to ignore the in between cells?
 

Hello people,

I have problem creating a formula that need to do the following:

(A and B represent the columns, 1 through 7 are rows)
- |A B
1 |5 s
2 |7
3 |5 b
4 |9
5 |3 b
6 |5
7 |6 s

If in column B there is "s" letter, the formula has to find the first "b" letter after the last "s", and to subtract from column A the first "b" from the last "s" (in the example A7-A3), and to ignore the in between "b" letters (in the example above there is one "b" letter in between, but there might be more than one in some cases)

Thank you. I hope someone can make my day.
baba