include Math def bigf(n) num = 0.0 den = 0.0 for i in 1 .. n num += 0.81 ** i den += 0.9 ** i end sqrt(num) / den end def f(n) finf = bigf(400) 1200.0 * (bigf(n) - finf) / (bigf(1) - finf) end n = gets.to_i s = Array.new(n) for i in 0 ... n s[i] = gets.to_f end num = 0.0 den = 0.0 for i in 1 .. n num += 2.0 ** (s[i - 1] / 800.0) * 0.9 ** i den += 0.9 ** i end rating = num / den rating = 800.0 * log2(rating) rating -= f(n) puts rating.to_i