def add_leading_zero(number: int, digit_num: int = 2) -> str:
    """add_leading_zero function

    Args:
        number (int): number that you want to add leading zero
        digit_num (int): number of digits that you want fill up to. Defaults to 2.

    Returns:
        str: number that has the leading zero

    Examples:
        >>> add_leading_zero(5, 3)
        "005"
    """
    return str(number).zfill(digit_num)