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: A 45 - year - old man , an admitted frequent cocaine user , presented to the Emergency Department ( ED ) on two separate occasions with a history of priapism after cocaine use .
### Output Text:
A 45 - year - old man , an admitted frequent <span class="chemical">cocaine</span> user , presented to the Emergency Department ( ED ) on two separate occasions with a history of priapism after <span class="chemical">cocaine</span> use . 