def dfs(i, w_sum)
	if w_sum == @w.inject(:+) / 2.0
		puts "possible"
		exit
	elsif w_sum > @w.inject(:+) / 2.0
		return
	end
	if i >= @w.length
		return
	end
	dfs(i + 1, w_sum)
	dfs(i + 1, w_sum + @w[i])
end

n = gets.strip.to_i
@w = gets.strip.split(' ').map(&:to_i).sort{|a, b| b <=> a }
dfs(0, 0)
puts "impossible"