public function advance($step = 1, $redraw = false)
    {
        parent::advance($step, $redraw);

        $this->current += $step;

        $percent = 0;
        if ($this->max > 0) {
            $percent = (float) $this->current / $this->max;
        }
        $this->output->write(sprintf('%d%%', floor($percent * 100)));
    }