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: RESULTS : Olanzapine - treated patients demonstrated a statistically significant greater mean ( + / - SD ) improvement in Y - MRS total score than placebo - treated patients ( - 14 . 8 + / - 12 . 5 and - 8 . 1 + / - 12 . 7 , respectively ; P < . 001 ) , which was evident at the first postbaseline observation 1 week after randomization and was maintained throughout the study ( last observation carried forward ) .
### Output Text:
RESULTS : <span class="chemical">Olanzapine</span> - treated patients demonstrated a statistically significant greater mean ( + / - SD ) improvement in Y - MRS total score than placebo - treated patients ( - 14 . 8 + / - 12 . 5 and - 8 . 1 + / - 12 . 7 , respectively ; P < . 001 ) , which was evident at the first postbaseline observation 1 week after randomization and was maintained throughout the study ( last observation carried forward ) . 