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: rTMS at 1 Hz was observed to markedly reduce drug - induced dyskinesias , whereas 5 - Hz rTMS induced a slight but not significant increase .
### Output Text:
rTMS at 1 Hz was observed to markedly reduce drug - induced dyskinesias , whereas 5 - Hz rTMS induced a slight but not significant increase . 