def this_extra_edition_number(edicao):
    """
    Gets a string 'edicao' that states which is this DOU's edition 
    (e.g. 132-B or 154) and returns the number (int) of extra editions up
    to this current one. No extra editions (e.g. 154) is 0, first
    extra edition (134-A) is 1, and so on.
    """
    last_char = str(edicao)[-1]
    if last_char.isdigit():
        return 0
    else:
        return ord(last_char.lower()) - 96