def extract_class_label(filename):
    """
    arg:
        filename: string, e.g.
        'images/001.Black_footed_Albatross/Black_footed_Albatross_0001_2950163169.jpg'

    return:
        A class label as integer, e.g. 1
    """
    _, class_dir, _ = filename.split("/")
    return int(class_dir.split(".")[0])