#include<bits/stdc++.h>
using namespace std;  
typedef long long ll;
typedef vector<int> vi;
typedef vector<vi> vvi;
#define rep(i,n) for(ll i=0;i<(n);i++)  
#define pii pair<int,int>
#define piii pair<int,pii>
#define mp make_pair
#define pb push_back  
#define ALL(a) (a).begin(),(a).end()
#define FST first
#define SEC second  
const int INF = (INT_MAX/2);
const ll LLINF = (LLONG_MAX/2);
const double eps = 1e-14;
const double PI = M_PI;  
#define DEB cout<<"!"<<endl
#define SHOW(a,b) cout<<(a)<<" "<<(b)<<endl
#define SHOWARRAY(ar,i,j) REP(a,i)REP(b,j)cout<<ar[a][b]<<((b==j-1)?((a==i-1)?("\n\n"):("\n")):(" "))
  
#define DIV 1000000007
typedef vector<ll> Array;
typedef vector<Array> matrix;

int main(){
  string s; cin >> s;
  int flag = 0;
  rep(i,s.size()){
    if(!(s[i] >= 'a' && s[i] <= 'm')){
      cout << "Impossible" << endl;
      return 0;
    }
  }
  
  for(char c = 'a'; c <= 'm'; c++){
    string ts = s;
    ts += c;
    vi v(100);
    rep(i,ts.size()){
      v[ts[i]-'a']++;
    }
    sort(ALL(v),greater<int>());
    if(v[0] == 2 && v[1] == 1 && v[12] == 1){
      cout << c << endl;
      flag++;
    }
  }
  if(!flag)
    cout << "Impossible"<<endl;
  return 0;
}