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: After one year of treatment , five of the remaining nine patients showed either partial ( n = 3 ) or complete ( n = 2 ) gall stone dissolution , suggesting that their stones were cholesterol rich .
### Output Text:
After one year of treatment , five of the remaining nine patients showed either partial ( n = 3 ) or complete ( n = 2 ) gall stone dissolution , suggesting that their stones were <span class="chemical">cholesterol</span> rich . 