how to do this

Hi Friends ,

I want to change xml given below

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<ZooConfiguration
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:noNamespaceSchemaLocation="..\..\..\schema\Zoo.xsd">
  <Configuration id="default">
    <AnnouncementOrder>
      <Announcement>Donkey</Announcement>
      <Announcement>Lion</Announcement>
      <Announcement>Snake</Announcement>
      <Announcement>Zebra</Announcement>
    </AnnouncementOrder>
  </Configuration>
</ZooConfiguration>


Condition is that if any one of (Elephant,Monkey) is there , donot
change any thing in xml . If none of (Elephant,monkey) present then
add both (Elephant,monkey) in sequence .

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<ZooConfiguration
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:noNamespaceSchemaLocation="..\..\..\schema\Zoo.xsd">
  <Configuration id="default">
    <AnnouncementOrder>
      <Announcement>Donkey</Announcement>
      <Announcement>Lion</Announcement>
      <Announcement>Snake</Announcement>
      <Announcement>Zebra</Announcement>
      <Announcement>Elephant</Announcement>
      <Announcement>Monkey</Announcement>
    </AnnouncementOrder>
  </Configuration>
</ZooConfiguration>

thanks
Amit singh