defmodule Main do 
  def main do
    _ = IO.gets("")
    IO.gets("") |> String.trim |> String.split |> Enum.map(&String.to_integer/1) |> Enum.sort(&(&1 >= &2)) |> put_on(0,0) |> out |> IO.puts
  end
  
  def put_on([], left, right) do
    [left, right]
  end
  
  def put_on([head|tail], left, right) when left >= right do
    put_on(tail, left, right+head)
  end
  
  def put_on([head|tail], left, right) do
    put_on(tail, left+head, right)
  end
  
  def out([left, right]) do
    if left == right, do: "possible", else: "impossible"
  end
end