import math


def lognormal_mean(m, stddev):
    """ compute mean of log x with mean and std. of x
    Args:
        m: mean of x
        stddev: standard deviation of x

    Returns: mean of log x

    """
    return math.log(m) - (0.5 * math.log(1.0 + (stddev * stddev) / (m * m)))