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: In patients without cocaine use , coronary computerized tomography angiography ( CTA ) has been shown to be useful for identifying a group of patients at low risk for cardiac events who can be safely discharged .
### Output Text:
In patients without <span class="chemical">cocaine</span> use , coronary computerized tomography angiography ( CTA ) has been shown to be useful for identifying a group of patients at low risk for cardiac events who can be safely discharged . 