gets
NS = gets.split.map(&:to_i).sort
SUM = NS.inject(&:+)
Q, R = SUM.divmod(2)
if R == 0 then
  h = {}
  h[0] = true

  while n = NS.shift do
    add = {}
    h.each do |k, v|
      next if k + n > Q
      add[k + n] = true
    end
    h.update add
  end

  puts h[Q] ? "possible" : "impossible"
else
  puts "impossible"
end