n = gets.to_i
a = gets.chomp.split.map(&:to_i)
c = 0
n.times do |i|
  b = a.rotate(i).dup
  x = b.shift
  y = 0
  b.each do |j|
    if x < y
      x += j
    else
      y += j
    end
  end
  c +=1 if x == y
  break if c > 0
end
puts c == 1 ? "possible" : "impossible"