def der_order(order: int) -> str:
    """Return correct suffix for order.

    >>> der_order(1)
    ... "1-st"
    >>> der_order(4)
    ... "4-th"
    """
    _suffix = ["st", "nd", "rd"]
    if order - 1 > 3:
        return f"{order}-th"
    else:
        return f"{order}-{_suffix[order - 1]}"