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Antonios Gkioulmpas ( also Antonios Gioulbas , ; born April 17 , 1986 in Marousi ) is a retired Greek swimmer , who specialized in backstroke events .
 Marousi
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Marousi