N = gets.to_i
perfs = N.times.map { gets.to_i }

def lf(n)
  a = 0
  b = 0
  1.upto(n) do |i|
    a += 0.81 ** i
    b += 0.9 ** i
  end

  Rational(Math.sqrt(a), b)
end

def f(n)
  a = Math.sqrt(Rational(0.81, 0.19))
  b = Rational(0.9, 0.1)
  inf_f = Rational(a, b)

  Rational(lf(n) - inf_f, lf(1) - inf_f) * 1200
end

def g(x)
  2.0 ** Rational(x, 800)
end

def rg(x)
  800 * Math.log2(x)
end

a = 0
b = 0

1.upto(N) do |i|
  a += g(perfs[i - 1]) * (0.9 ** i)
  b += 0.9 ** i
end

rate = rg(Rational(a, b)) - f(N)
puts rate.ceil