#define _USE_MATH_DEFINES
#include  <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
#include <string>
#include<math.h>
#include<iomanip>
#include<stdio.h>
#include <stdlib.h>
#include<stdio.h>
#include <queue>
#include<map>
#include <sstream>
#include<set>
#include<stack>

//#include<bits/stdc++.h>


using namespace std;



int main() {
	
	
	string p;
	cin >> p;
	map<char, int>r;

	sort(p.begin(), p.end());

	for (int i = 0; i < p.size(); i++) {
		r[p[i]]++;
	}
	vector<char>t;
	for (char i = 'a'; i <= 'm'; i++) {
		if (!r[i])t.push_back(i);
	}
	if (t.size() >= 2)cout << "Impossible" << endl;
	else if (t.size() == 1)cout << t[0] << endl;
	else {
		for (char i = 'a'; i <= 'm'; i++)cout << i << endl;
	}
	
	return 0;


		
}