n = gets.chomp.to_i
w = gets.chomp.split(' ').map {|i| i.to_i}
total = w.inject(:+)
if total % 2 == 1
	puts 'impossible'
	exit
end
(n/2).downto(1).each do |i|
	w.combination(i) do |set|
		if total.to_f / 2 - set.inject(:+) == 0
			puts 'possible'
			exit
		end
	end
end
puts 'impossible'