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: Organic mental disorder was observed in a 29 - year - old female in the prognostic period after the onset of carmofur - induced leukoencephalopathy .
### Output Text:
Organic mental disorder was observed in a 29 - year - old female in the prognostic period after the onset of <span class="chemical">carmofur</span> - induced leukoencephalopathy . 