#include <vector> 
#include <list> 
 #include <map>
 #include <set>
#include <deque>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>
#include <queue>
using namespace std;

//conversion
//------------------------------------------
inline int toInt(string s) {int v; istringstream sin(s);sin>>v;return v;}
template<class T> inline string toString(T x) {ostringstream sout;sout<<x;return sout.str();}

//math
//-------------------------------------------
template<class T> inline T sqr(T x) {return x*x;}

//typedef
//------------------------------------------
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef long long LL;

//container util
//------------------------------------------
#define ALL(a)  (a).begin(),(a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define MP make_pair
#define SZ(a) int((a).size())
#define EACH(i,c) for(typeof((c).begin()) i=(c).begin(); i!=(c).end(); ++i)
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort((c).begin(),(c).end())

//repetition
//------------------------------------------
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n)  FOR(i,0,n)

//constant
//--------------------------------------------
const double EPS = 1e-10;
const double PI  = acos(-1.0);

//clear memory
#define CLR(a) memset((a), 0 ,sizeof(a))

//debug
#define dump(x)  cerr << #x << '=' << (x) << endl;
#define debug(x) cerr << #x << '=' << (x) << '('<<'L' << __LINE__ << ')' << ' ' << __FILE__ << endl;

int main(){
    

    multiset<char> st;
    string s;
    cin>>s;
    // for(char a='a';a<='z';a++){
    //     //cout<<a<<endl;
    // }

    REP(i,SZ(s)){
        char a=s[i];
        st.insert(a);
    }
    char ans='0';

    char twoindex='0';
    char zeroindex='0';
    vector<char> oneindex;

    for(char a='z';a>='a';a--){

        if(a>'m'){
           if( st.count(a)>1){
               cout<<"Impossible"<<endl;
               return 0;
           }
        }
        else{
            if( st.count(a)==1){
                
                oneindex.push_back(a);
           }
           else if(st.count(a)==2){
                if(twoindex!='0'){
                   cout<<"Impossible"<<endl;
                    return 0;
               }
               twoindex=a;
           }
           else if(st.count(a)==0){

               if(zeroindex!='0'){
                   cout<<"Impossible"<<endl;
                    return 0;
               }
               zeroindex=a;
           }
        }
    }

    if(twoindex!='0'){
        if(zeroindex!='0'){
            cout<<zeroindex<<endl;
            return 0;
        }
        else{
            cout<<"Impossible"<<endl;
                    return 0;
        }
    }
    else{
        if(zeroindex!='0'){
            cout<<"Impossible"<<endl;
            return 0;
        }
        if(oneindex.size()==0){
            cout<<"Impossible"<<endl;
            return 0;
        }
        REP(i,SZ(oneindex)){
            cout<<oneindex[oneindex.size()-1- i]<<endl;
        }
        return 0;
    }


}