#include<iostream>
#include<map>
#include<string>
#include<vector>
#include<algorithm>
#include<numeric>
#include<cmath>
#include<queue>
using namespace std;
long long int inf = 10000000000;

int main(){

  string s;
  cin >> s;
  vector<int> c(13, 0);
  for(int i=0; i<s.size(); i++){
    if( s[i] < 'a' || s[i] > 'z' ){
      cout << "Impossible" << endl;
      return 0;
    }
    c[ s[i]-'a' ]++;
  }
  bool w = false;
  for(int i=0; i<13; i++){
    bool t = false;
    int f = 0;
    c[i]++;
    for(int j=0; j<13; j++){
      if( c[j] == 2 ) t = true;
      else if( c[j] == 1 ) f++;
    }
    c[i]--;
    char q = 'a' + i;
    if( t && f == 12 ){
      cout << q << endl;
      w = true;
    }
  }
  if(!w) cout << "Impossible" << endl;
  return 0;
}





// EOF