write nth occurence of each value in pandas series

Question

I would like to see the nth occurrence of each value in a pandas series. For example I have a series as shown below:

    pd.DataFrame(pd.Series(['a', 'a', 'b', 'c', 'a', 'b', 'a', 'a', 'b', 'c', 'b', 'b'], name='A'))

    A
0   a
1   a
2   b
3   c
4   a
5   b
6   a
7   a
8   b
9   c
10  b
11  b

B being the occurrence count from top to bottom, I would like to see the dataframe below:

    A   B
0   a   1
1   a   2
2   b   1
3   c   1
4   a   3
5   b   2
6   a   4
7   a   5
8   b   3
9   c   2
10  b   4
11  b   5