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In 1795 he entered the service of the admiralty board of architecture ; as the assistant to Brenna , together with whom , it is assumed , he participated in the construction of Saint Michael 's Castle in Saint Petersburg .
 Brenna, Petersburg
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Brenna, Petersburg