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: Olanzapine - treated patients demonstrated a higher rate of response ( 65 % vs 43 % , respectively ; P = . 02 ) and euthymia ( 61 % vs 36 % , respectively ; P = . 01 ) than placebo - treated patients .
### Output Text:
<span class="chemical">Olanzapine</span> - treated patients demonstrated a higher rate of response ( 65 % vs 43 % , respectively ; P = . 02 ) and euthymia ( 61 % vs 36 % , respectively ; P = . 01 ) than placebo - treated patients . 