#include<bits/stdc++.h>
#define MAX_N 100001
#define INF_INT 2147483647
#define INF_LL 9223372036854775807
#define REP(i,n) for(int i=0;i<(int)(n);i++)
using namespace std;
typedef long long int ll;
typedef pair<ll,ll> P;

bool isPrime(int n){
  if(n == 2)
    return true;
  if(n % 2 == 0)
    return false;
  int sqr = sqrt(n)+1;
  for(int i=3;i<=sqr;i++){
    if(n % i == 0)
      return false;
  }
  return true;
}

bool cmp(pair<int,string> a,pair<int,string> b){
  if(a == b)
    return true;
  else if(a.first < b.first)
    return true;
  else if(a.first > b.first)
    return false;
  else if(a.second > b.second)
    return true;
  else
    return false;
}
bool cmpf(pair<int,string> a,pair<int,string> b){
  return a.first > b.first;
}
bool cmps(pair<int,string> a,pair<int,string> b){
  return a.second < b.second;
}


int main()
{
  int A=0,B=0,res=0,l=0;
  bool twf=false;
  char a;
  map<char,int> mp;
  string S;
  cin >> S;
  REP(i,S.size()){
   
    mp[S[i]]++;
    if(mp[S[i]] >= 3 || S[i] > 'm'){
      cout << "Impossible" << endl;
      return 0;
    }
  }
  for(char i='a';i<='m';i+=1){
    if(mp[i] == 2){
      if(twf){
        cout << "Impossible" << endl;
        return 0;
      }
      twf = true;
    }
    if(mp[i] == 0){
      a = i;
    }
  }
  if(twf){
    cout << a << endl;
  }else{
    for(char i='a';i<='m';i++){
      cout << i << endl;
    }
  }
 
  
  return 0;
}