Trying to count the number of changes from one number to another in a single column

[nielsent]

So I have a column of data that is 25,000 cells long, and each cell has a one or a zero in it. I want to know how many times it changes from one to zero and vice versa. I don't know if there is a quick formula for this for if it is a VBA macro to make it happen. But any help would be appreciated. I have included a quick example showing what the input column "A" would look like and the desired output column "B" should read.

A B
-----
1 |0 0
2 |0 0
3 |1 1
4 |0 2
5 |0 2
6 |0 2
7 |1 3
8 |1 3
9 |0 4

[FDibbins]

In C2, copied down...
=IF(A2=A1,C1,C1+1)