protected function parseArithmeticResponse($buffer, array $lines)
    {
        // Extract meta-data
        $metaData = explode(self::COMMAND_SEPARATOR, $lines[0]);

        // Check buffer for failure response
        if ($buffer === self::RESPONSE_NOT_FOUND . self::COMMAND_TERMINATOR) {
            $result = $this->setLastResponse(self::MEMCACHED_NOTFOUND);

        } else {
            // Insert the response (= new value) as result
            $result = (float)$metaData[0];
        }

        return $result;
    }