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He is also remembered as the friend of Rigas Feraios , a Greek revolutionary poet , whom he tried to rescue from the Ottoman authorities in Belgrade .
 Rigas Feraios, Ottoman, Belgrade
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Rigas Feraios, Ottoman, Belgrade