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: Thirty - nine ( 30 % ) of flumazenil - treated patients , compared with 17 ( 25 % ) of placebo - treated patients had one or more drug - related adverse experiences .
### Output Text:
Thirty - nine ( 30 % ) of <span class="chemical">flumazenil</span> - treated patients , compared with 17 ( 25 % ) of placebo - treated patients had one or more drug - related adverse experiences . 