fun main( args : Array<String> ) {
  val a = readLine()!!
  "abcdefghijklm".map { x ->
    (a + x.toString()).groupBy {
      it
    }.map { 
      val (k, arr) = it
      arr.size
    }.sortedBy { it }.let {
      it == listOf(1,1,1,1,1,1,1,1,1,1,1,1,2)
    }.let { 
      Pair(x, it)
    }
  }.filter {
    it.second == true
  }.let { 
    when { 
      it.size >= 1 -> it.map { println(it.first)  } 
      else -> println("Impossible")
    }
  }
}