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: There was no significant difference between occupancy levels obtained with haloperidol or risperidone .
### Output Text:
There was no significant difference between occupancy levels obtained with <span class="chemical">haloperidol</span> or <span class="chemical">risperidone</span> . 