#include <bits/stdc++.h>
// #include <atcoder/all>
using namespace std;
// using namespace atcoder;
#define rep(i, a) for (int i = 0; i < (int)(a); i++)
#define sz(x) (int)(x).size()
#define pcnt __builtin_popcountll
typedef long long ll;
template<typename T>istream& operator>>(istream&i,vector<T>&v){rep(j,sz(v))i>>v[j];return i;}
template<typename T>string join(const vector<T>&v){stringstream s;rep(i,sz(v))s<<' '<<v[i];return s.str().substr(1);}
template<typename T>ostream& operator<<(ostream&o,const vector<T>&v){if(sz(v))o<<join(v);return o;}
template<typename T1,typename T2>istream& operator>>(istream&i,pair<T1,T2>&v){return i>>v.first>>v.second;}
template<typename T1,typename T2>ostream& operator<<(ostream&o,const pair<T1,T2>&v){return o<<v.first<<","<<v.second;}
template<typename T>bool mins(T& x,const T&y){if(x>y){x=y;return true;}else return false;}
template<typename T>bool maxs(T& x,const T&y){if(x<y){x=y;return true;}else return false;}
template<typename T>ll suma(const vector<T>&a){ll res(0);for(auto&&x:a)res+=x;return res;}

#ifdef _DEBUG
inline void dump() { cerr << endl; }
template <typename Head> void dump(Head &&head) { cerr << head; dump(); }
template <typename Head, typename... Tail> void dump(Head &&head, Tail &&... tail) { cerr << head << ", "; dump(forward<Tail>(tail)...); }
#define debug(...) do { cerr << __LINE__ << ":\t" << #__VA_ARGS__ << " = "; dump(__VA_ARGS__); } while (false)
#else
#define dump(...)
#define debug(...)
#endif

template <typename T> struct edge {
  int src, to;
  T cost;
  edge(int to, T cost) : src(-1), to(to), cost(cost) {}
  edge(int src, int to, T cost) : src(src), to(to), cost(cost) {}
  edge &operator=(const int &x) {
    to = x;
    return *this;
  }
  operator int() const { return to; }
};
template <typename T> using Edges = vector<edge<T>>;
template <typename T> using WeightedGraph = vector<Edges<T>>;
using UnWeightedGraph = vector<vector<int>>;
template <typename T> using Matrix = vector<vector<T>>;

const ll LINF = 1LL << 60;
const int INF = 1001001001;

/////////////////////////////////////////////////////////////////////

int main()
{
  string s; cin>>s;
  sort(s.begin(),s.end());

  if (s == "abcdefghijklm") {
    rep(i, 13) cout << char(i+'a') << "\n";
    return 0;
  }

  vector<int> cnt(26);
  for (auto c:s) {
    int a = c-'a';
    cnt[a]++;
  }

  vector<int> t(3);
  int tar = -1;
  rep(i, 13) {
    if (cnt[i] > 2) {
      cout << "Impossible" << "\n";
      return 0;
    }
    t[cnt[i]]++;
    if (cnt[i] == 0) tar = i;
  }
  if (t[0] == 1 && t[2] == 1) cout << char(tar+'a') << "\n";
  else cout << "Impossible" << "\n";

  return 0;
}