N = gets.to_i
A = gets.split.map(&:to_i).sort
C = A.tally
C.default = 0

ans = 0

def f(nums)
  c = nums.tally
  c.default = 0
  m = nums.max

  0.upto(m) do |x|
    return [false, x] if c[x] <= 1
  end

  [true, m + 1]
end

res, v = f(A)

if res
  puts v
else
  idx = A.rindex { |a| a > v }

  if idx.nil?
    puts v
  else
    A[idx] = v

    _, v = f(A)

    puts v
  end
end