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: Improvement of levodopa - induced dyskinesia by propranolol in Parkinson ' s disease .
### Output Text:
Improvement of <span class="chemical">levodopa</span> - induced dyskinesia by <span class="chemical">propranolol</span> in Parkinson ' s disease . 