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: Significantly more weight gain occurred with olanzapine than with risperidone : the increase in weight at 4 months relative to baseline weight was 17 . 3 % ( 95 % CI = 14 . 2 % - 20 . 5 % ) with olanzapine and 11 . 3 % ( 95 % CI = 8 . 4 % - 14 . 3 % ) with risperidone .
### Output Text:
Significantly more weight gain occurred with <span class="chemical">olanzapine</span> than with <span class="chemical">risperidone</span> : the increase in weight at 4 months relative to baseline weight was 17 . 3 % ( 95 % CI = 14 . 2 % - 20 . 5 % ) with <span class="chemical">olanzapine</span> and 11 . 3 % ( 95 % CI = 8 . 4 % - 14 . 3 % ) with <span class="chemical">risperidone</span> . 