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: CONCLUSION : Only one hypersensitivity reaction to CE was documented among 9 P and N - highly NSAIDs intolerant patients .
### Output Text:
CONCLUSION : Only one hypersensitivity reaction to <span class="chemical">CE</span> was documented among 9 <span class="chemical">P</span> and <span class="chemical">N</span> - highly NSAIDs intolerant patients . 