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Governors Alaska was purchased by the United States from Russia in 1867 , with formal transfer occurring on October 18 , 1867 , which is now celebrated as Alaska Day .
 Alaska, United States, Russia, Alaska
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Alaska, United States, Russia, Alaska