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: For further reduction of HIT type II , the use of intravenous heparin should be avoided and the prophylactic anticoagulation should be performed with low - molecular - weight heparin after normalization of platelet count .
### Output Text:
For further reduction of HIT type II , the use of intravenous <span class="chemical">heparin</span> should be avoided and the prophylactic anticoagulation should be performed with low - molecular - weight <span class="chemical">heparin</span> after normalization of platelet count . 