$finf = Math.sqrt(100.0 / 19 - 1) / 9.0
def F(n)
  d = 0.0
  c = 0.0
  (1..n).each do |i|
    d += 0.81 ** i
    c += 0.9 ** i
  end
  d = Math.sqrt(d)
  d / c
end

def f(n)
  (F(n) - $finf) / (F(1) - $finf) * 1200.0
end

def g(x)
  2.0 ** (x / 800.0)
end

def gi(y)
  Math.log(y) / Math.log(2) * 800
end

def rating(n, rs)
  d = 0.0
  c = 0.0
  (1..n).each do |i|
    d += g(rs[i-1]) * (0.9 ** i)
    c += 0.9 ** i
  end
  gi(d/c) - f(n)
end

n = gets.to_i
xs = []
(0..n-1).each do |i|
  x = gets.to_f
  xs << x
end

puts rating(n, xs).to_i