add pandas series values to new dataframe column at end of pandas dataframe

Question

I have a dataframe with values like this:

    A | B | C 
0 | 1 | 2 | 3
1 | 1 | 4 | 2
2 | 3 | 3 | 1
3 | 5 | 2 | 4
4 | 3 | 1 | 3

And a series w