import java.util.HashSet;
import java.util.Scanner;
import java.util.stream.IntStream;

public class Main{
	static IntStream REPS(int v){return IntStream.range(0,v);}
	static IntStream REPS(int l,int r){return IntStream.rangeClosed(l,r);}
	static IntStream INS(int n) {return REPS(n).map(i->getInt());}
	static Scanner s=new Scanner(System.in);
	static int getInt(){return Integer.parseInt(s.next());}

	public static void main(String[]$){
		HashSet<Integer>r=new HashSet<>();
		"abcdefghijklm".chars().forEach(r::add);
		s.next().chars().forEach(r::remove);

		if(r.size()==1)
			System.out.println((char)(int)r.stream().findAny().get());
		else if(r.isEmpty())
			"abcdefghijklm".chars().mapToObj(i->(char)i).forEach(System.out::println);
		else
			System.out.println("Impossible");
	}
}