import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.PriorityQueue;
import java.util.Scanner;

public class Main {
	
	public static long MOD = 1000000007;
	
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		final char[] ops = "abcdefghijklm".toCharArray();
		final char[] chs = sc.next().toCharArray();
		
		int[] count = new int[26];
		for(final char ch : chs){
			count[ch - 'a']++;
		}
		
		int one_count = 0, two_count = 0;
		for(final char op : ops){
			final int index = op - 'a';
			
			if(count[index] == 1){
				one_count++;
			}else if(count[index] == 2){
				two_count++;
			}
		}
		
		//System.out.println(Arrays.toString(count) + " " + one_count + " " + chs.length);
		
		if(two_count >= 2){
			System.out.println("Impossible");
		}else if(two_count == 1 && one_count == ops.length - 2){
			for(final char op : ops){
				final int index = op - 'a';
				if(count[index] == 0){
					System.out.println(op);
					break;
				}
			}
		}else if(two_count == 0 && one_count == ops.length){
			for(final char op : ops){
				System.out.println(op);
			}
		}else{
			System.out.println("Impossible");
		}
		
	}
}