def logistic_est_loss_deriv(y_est, y):
    """
    Compute the derivative of the logistic loss with
    respect to its input variable, given only the 
    output y_est of the logistic function

    Parameters
    ----------
    y_est: float
        Estimated output of the logistic function
    y: float
        Target value
    
    Returns
    -------
    float:
        Derivative of logistic loss with respect to input
        *u* to logistic function
    """
    return y_est-y