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: Thirty - six nonobese subjects with schizophrenia or schizoaffective disorder , matched by body mass index and treated with either clozapine , olanzapine , or risperidone , were included in the analysis .
### Output Text:
Thirty - six nonobese subjects with schizophrenia or schizoaffective disorder , matched by body mass index and treated with either <span class="chemical">clozapine</span> , <span class="chemical">olanzapine</span> , or <span class="chemical">risperidone</span> , were included in the analysis . 