# frozen_string_literal: true

x = gets.chomp.chars.map(&:to_i).sort.permutation.to_a

largest = x[-1].map(&:to_s).join.to_i

if x[-2][0].zero?
  p(-1)
  exit
end
candidate = x[-2].map(&:to_s).join.to_i

if candidate
  if candidate == largest
    p(-1)
  else
    p candidate
  end
else
  p(-1)
end