import re


def find_surnames(authors):
    """
    Make assumption that all authors are given as surname and initials,
    so any uppercase followed by one-or-more lowercase letters is a surname.
    """
    surname_list = []
    surname_regex = "([A-Z\u00C0-\u00DE][a-z\u00DF-\u00FF\u0107]+)+"
    if isinstance(authors, str):
        surname_list = re.findall(surname_regex, authors)
        return surname_list
    elif isinstance(authors, list) or isinstance(authors, tuple):
        for author in authors:
            surname_list += re.findall(surname_regex, author)
    return surname_list