X = Math.sqrt(4.263158) / 9.0
def f_(n)
	Math.sqrt((1..n).sum { 0.81**_1 }) / (1..n).sum { 0.9**_1 }
end
def f(n)
	(f_(n) - X) / (f_(1) - X) * 1200
end
def g(x)
	2.0**(x / 800.0)
end
def g_(x)
	800 * Math.log10(x) / Math.log10(2)
end

n = gets.to_i
a = (1..n).map { gets.to_f }
val = (1..n).sum { |i| g(a[i - 1]) * 0.9**i } / (1..n).sum { 0.9**_1 }
ans = g_(val) - f(n)
puts ans.round