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The total development time had been around half a year , with a cost of around US $ 25,000 to cover the team 's rent and US $ 750 per month salaries , plus around US $ 6,500 for the computer John Carmack used to develop the engine and the US $ 5,000 to get the " Wolfenstein " copyright .
 John Carmack
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 John Carmack