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: Repetitive transcranial magnetic stimulation for levodopa - induced dyskinesias in Parkinson ' s disease .
### Output Text:
Repetitive transcranial magnetic stimulation for <span class="chemical">levodopa</span> - induced dyskinesias in Parkinson ' s disease . 