$n = gets.to_i
$w = gets.split.map(&:to_i)
$nerai = $w.inject(:+)/2.0
$flag = "impossible"

def dfs(depth, total)
  if depth >= $n - 1
    return $w[depth]
  end

  a = dfs(depth+1, total+$w[depth])
  b = dfs(depth+1, total)

  return a if $nerai - a == 0
  return b if $nerai - b == 0
  return -1
end

puts dfs(-1, 0) > 0 ? "possible" : "impossible"