fun main(args: Array<String>) {
  readLine()!!.toInt()
  val a = readLine()!!.split(" ").map { it.toInt() }
  val mn = a.min()!!
  val mx = a.max()!!
  val c = a.count { it == mn }
  var ans = true
  if (mn == 1) {
    if (c == 2) {
      if (mn != mx) ans = false
    } else {
      if (c > 2 || mn * 2 != mx) ans = false
    }
  } else {
    if (c == 1) {
      if (2 * mn != mx) ans = false
    } else if (c == 2) {
      if (2 * mn - 1 != mx) ans = false
    } else {
      ans = false
    }
    for (i in mn + 1..mx) {
      if (a.count { it == i } < 2) ans = false
    }
  }
  println(if (ans) "Possible" else "Impossible")
}
