def turn_back(dirs: dict):
    """ Make a new dict with a structure:
        dict(
            list_1_elem_1: key_1, list_1_elem_2: key_1, list_1_elem_2: key_1,
            list_2_elem_1: key_2, list_2_elem_2: key_2
            etc..
        )
    """
    proper_dict = {}
    for key, values in dirs.items():
        for value in values:
            proper_dict[value.lower()] = key
    return proper_dict