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: Of the patients at the Drug Addiction Service in the municipal of Copenhagen , 450 ( approximately 52 % ) were included .
### Output Text:
Of the patients at the Drug Addiction Service in the municipal of Copenhagen , 450 ( approximately 52 % ) were included . 