import java.util.Arrays;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.Scanner;

public class Main {
	
	public static long MOD = 1000000007;
	
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		char[] alpha = new char[26];
		for(final char ch : sc.next().toCharArray()){
			alpha[ch - 'a']++;
		}
		
		int two_count = 0, one_count = 0;
		for(final int a : alpha){
			if(a == 2){ 
				two_count++;
			}else if(a == 1){
				one_count++;
			}
		}
		
		if(two_count == 6 && one_count == 1){
			for(int i = 0; i < 26; i++){
				if(alpha[i] == 1){
					System.out.println((char)(i + 'a'));
					return;
				}
			}
		}else{
			System.out.println("Impossible");
		}
	}
}