import java.util.Scanner

class No548() {
	var array = mutableListOf('a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm')
	var input = Scanner(System. `in`).next()

	fun differenceSet(): MutableList<Char> {
		input.forEach { array.remove(it) }
		return array
	}

	fun judge(){
		var except = differenceSet()
		if (except.size > 1) println("Impossible")
		else if (except.size == 0) println("a\nb\nc\nd\ne\nf\ng\nh\ni\nj\nk\nl\nm")
		else println(except[0])
	}
}

fun main(args: Array<String>){
	var no548 = No548()
	no548.judge()
}