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: The typical signs of VPA - induced encephalopathy are impaired consciousness , sometimes marked EEG background slowing , increased seizure frequency , with or without hyperammonemia .
### Output Text:
The typical signs of <span class="chemical">VPA</span> - induced encephalopathy are impaired consciousness , sometimes marked EEG background slowing , increased seizure frequency , with or without hyperammonemia . 