import math


def get_ith_sub_dir_name(split_dir_index: int, num_split_dirs: int) -> str:
    """
    Get the ith split directory name. For instance, if split_dir_index == 10 and num_split_dirs == 100 then '010' will
    be returned.

    :param split_dir_index: Split directory index.
    :param num_split_dirs: Number of split directories.
    :return: Sub directory name.
    """

    num_zeros = int(math.floor(math.log10(num_split_dirs)) - math.floor(math.log10(split_dir_index)))
    return '0' * num_zeros + str(split_dir_index)