# frozen_string_literal: true

def solve
  A.zip(rates).map { _1 * _2 }.sum
end

def rates
  half.double
end

def half
  (0..(Rational(N, 2).ceil - 1)).map { (_1 + 1) * (N - _1) }
end

class Array
  def double
    self + (N.odd? ? self[0..-2] : self).reverse
  end
end

N = gets.to_i
A = gets.split.map(&:to_i)

puts solve