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