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: Body mass index at baseline and at 4 months was 24 . 3 ( 95 % CI = 22 . 8 - 25 . 7 ) versus 28 . 2 ( 95 % CI = 26 . 7 - 29 . 7 ) with olanzapine and 23 . 9 ( 95 % CI = 22 . 5 - 25 . 3 ) versus 26 . 7 ( 95 % CI = 25 . 2 - 28 . 2 ) with risperidone .
### Output Text:
Body mass index at baseline and at 4 months was 24 . 3 ( 95 % CI = 22 . 8 - 25 . 7 ) versus 28 . 2 ( 95 % CI = 26 . 7 - 29 . 7 ) with <span class="chemical">olanzapine</span> and 23 . 9 ( 95 % CI = 22 . 5 - 25 . 3 ) versus 26 . 7 ( 95 % CI = 25 . 2 - 28 . 2 ) with <span class="chemical">risperidone</span> . 