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

raise if A[0] != 0

c = [
  [0, [
    [1, [
      [4, []],
      [3, []]
    ]],
    [2, []]
  ]]
]

A.each do |i|
  x, y = c[i]
  puts x
  break unless y
  c = y
end