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However , according to Stalin biographer Robert Service , Stalin regretted allowing himself the ostentatious military title , and asked Winston Churchill to continue to refer to him as a marshal instead .
 Stalin, Robert Service, Stalin, Winston Churchill
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Stalin, Robert Service, Stalin, Winston Churchill