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: Congestive heart failure caused or contributed to death in 0 / 32 patients in Group 1 v 6 / 52 ( 12 % ) of patients in Group 2 ( P less than 0 . 25 ) .
### Output Text:
Congestive heart failure caused or contributed to death in 0 / 32 patients in Group 1 v 6 / 52 ( 12 % ) of patients in Group 2 ( P less than 0 . 25 ) . 