#define _USE_MATH_DEFINES
#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
#include<string>
#include<iostream>
#include<iostream>
#include<cctype>
#include<cstdio>
#include<vector>
#include<stack>
#include<queue>
#include <algorithm>
#include<math.h>
#include<set>
#include<map>
#include <sstream>
#include<iomanip>
#include <ctype.h>
using namespace std;

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

int main() {
	int g[18] = {};
	string p;
	cin >> p;
	sort(p.begin(), p.end());
	for (int i = 0; i < p.size(); i++) {
		if (p[i] > 'm') {
			cout << "Impossible" << endl;
			return 0;
		}
		g[p[i] - 'a']++;
		if(g[p[i] - 'a']>2) {
			cout << "Impossible" << endl;
			return 0;
		}
	}
	for (int i = 0; i <= 'm' - 'a'; i++) {
		if (g[i] == 0) { 
			cout << char(i+'a')  << endl;
		return 0;
		}
	}

	for (int i = 0; i <= 'm' - 'a'; i++) {
		
			cout << char('a' + i) << endl;
			
	}


	return 0;
}