57. A pile of balls, with red and yellow colors. First, 50 balls are taken out, of which 49 are red, and then every 8 balls taken out afterward contain exactly 7 red balls, until the last 8 balls are taken out, exactly finishing the pile. It is known that the red balls account for no less than $90 \%$ of the total balls taken out. How many balls are there in the pile at most? $\qquad$
Reference answer: 210