def ar(vi, vf, D=0, W=0):
    """The Arithmetic Return is the simplest way of calculating
    the rate of return on an investment. To calculate it,
    you need the amount of growth, which is simply the final value `Vf`
    minus the initial value `Vi`. Then you just divide the amount of growth
    by the initial amount.

    Args:
        vi: Initial value of investment
        vf: Final value of investment
        D: The total deposit made into the investment
        W: Total of any withdrawals

    Returns:
        The arithmetic return of a given investment.

    Example:
        By providing initial and final value of investment
        you can get the percentage return of your investment:

        >>> import malee
        >>> malee.ar(100, 140)
        0.4
    """
    return (vf - D + W - vi) / vi