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: Risperidone - associated , benign transient visual disturbances in schizophrenic patients with a past history of LSD abuse .
### Output Text:
<span class="chemical">Risperidone</span> - associated , benign transient visual disturbances in schizophrenic patients with a past history of <span class="chemical">LSD</span> abuse . 