How do I rid a string only from the beginning and only the end of the string?

I have a string that is pretty long, paragraphs long. It gets surrounded by div tags from another process. So my string always looks like this:

<div id="xxxx">blah balha ablah blahblah balha ablah blahblah balha ablah blahblah balha ablah blahblah balha ablah blahblah balha ablah blahblah balha ablah blah<div id="somethingelse">blah balha ablah blah</div>blah balha ablah blah<b>blah balha ablah blah</b>blah balha ablah blah</div>

Notice how there are surrounding div tags. I want to chop off the beginning <div id="xxxx"> and ending </div>. The xxx can be anything tho so it won't be hard coded. Considering the size of the string, what's an efficient way to do this?