N = gets.to_i
W = gets.split.map(&:to_i).sort!

sum = 0; W.each{ |w| sum += w }
if sum.odd?
  puts 'impossible'
  exit
end

half = sum / 2
candi = W.select{ |w| w <= half }
1.upto(N/2) do | cnt |
  candi.combination(cnt).to_a.each do | ws |
    sum = 0; ws.each{ |w| sum += w }
    if sum == half
      puts 'possible'
      exit
    end
  end
end
puts 'impossible'