C # library for (x) html matching

Curious if anyone has come across a C # library that will clean up invalid html. Basically, our CMS has some areas where we allow users to enter HTML and this invariably leads to incorrectly formatted code.

Example - if someone puts:

<div><span>blah blah blah</div>

      

        
        
        
      

    

We'd like to rip out any unfinished tags so that in the end:

<div>blah blah blah</div>

      

        
        
        
      

    

Hoping not to reinvent the wheel here.

Thanks!