fun main(args: Array<String>){
    val arr = readLine()!!.toList()
    when {
        arr.distinct().size == arr.size -> {
            arr.forEach{ println(it)}
        }
        arr.distinct().size + 1 == arr.size -> {
            val ans = "abcdefghijklm".toList().filter { !arr.contains(it) }!!.first()
            println(ans)
        }
        else -> println("Impossible")
    }
}