In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: BACKGROUND : Acetaminophen ( paracetamol - - P ) and Nimesulide ( N ) are widely used analgesic - antipyretic / anti - inflammatory drugs .
### Output Text:
BACKGROUND : <span class="chemical">Acetaminophen</span> ( <span class="chemical">paracetamol</span> - - <span class="chemical">P</span> ) and <span class="chemical">Nimesulide</span> ( <span class="chemical">N</span> ) are widely used analgesic - antipyretic / anti - inflammatory drugs . 