def find_biggest_box(length: int, width: int) -> int:
    """
    >>> find_biggest_box(1, 1)
    1
    >>> find_biggest_box(1680, 640)
    80
    >>> find_biggest_box(640, 1680)
    80
    """
    if length < width:
        length, width = width, length
    rest = length % width
    if not rest:
        return width
    return find_biggest_box(width, rest)