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: Baseline electrocardiogram abnormalities and market elevations not associated with myocardial necrosis make accurate diagnosis of myocardial infarction ( MI ) difficult in patients with cocaine - associated chest pain .
### Output Text:
Baseline electrocardiogram abnormalities and market elevations not associated with myocardial necrosis make accurate diagnosis of myocardial infarction ( MI ) difficult in patients with <span class="chemical">cocaine</span> - associated chest pain . 