inputs = STDIN.readlines.map(&:chomp)
N = inputs[0].to_i
Ws = inputs[1].split(/\s+/).map(&:to_i)

class Omori
  def initialize(weight)
    @weight = weight
  end

  attr_reader :weight
end

def check(k, omoris)
  do_next = false
  omoris.combination(k) do |os1|
    sum1 = os1.map(&:weight).inject(:+)
    sum2 = (omoris - os1).map(&:weight).inject(:+)
    do_next = true if sum1 > sum2
    return [true, false] if sum1 == sum2
  end
  [false, do_next]
end

def main(omoris)
  n = omoris.size / 2
  n.step(1, -1) do |k|
    result, do_next = check(k, omoris)
    return true if result
    break unless do_next
  end
  false
end

puts main(Ws.map { |w| Omori.new(w) }) ? 'possible' : 'impossible'