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From 2006 to 2010 he studied at the National School of Music Liubomir Pipkov ( Sofia , Bulgaria ) in the violin class of Prof. Blagorodna Taneva .
 Sofia
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Sofia