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: CONCLUSIONS : The excess of MB in warfarin users with ICH compared to other groups suggests that MB increase the risk of warfarin - associated ICH .
### Output Text:
CONCLUSIONS : The excess of MB in <span class="chemical">warfarin</span> users with ICH compared to other groups suggests that MB increase the risk of <span class="chemical">warfarin</span> - associated ICH . 