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 direct cost of treating clinically significant RIHA is 1 % ( 170 / 16 , 459 ) of drug treatment costs .
### Output Text:
CONCLUSIONS : The direct cost of treating clinically significant RIHA is 1 % ( 170 / 16 , 459 ) of drug treatment costs . 