#include <bits/stdc++.h>
using namespace std;

typedef long long ll;
#define REP(i,n) for(int i=0,_n=(int)(n);i<_n;++i)
#define ALL(v) (v).begin(),(v).end()
template<class T1,class T2>ostream& operator<<(ostream& os,const pair<T1,T2>&a){return os<<"("<<a.first<<","<<a.second<< ")";}
template<class T>void pv(T a,T b){for(T i=a;i!=b;++i)cout<<(*i)<<" ";cout<<endl;}
template<class T>bool chmin(T&a,const T&b){return a>b?(a=b,1):0;}
template<class T>bool chmax(T&a,const T&b){return a<b?(a=b,1):0;}


int nextInt() { int x; scanf("%d", &x); return x;}

int main2() {
  string s; cin >> s;
  int bin[26] = {};
  REP(i, s.size()) {
    ++bin[s[i]-'a'];
  }

  int two = 0;
  string ans = "";
  REP(i, 26) {
    if (bin[i] == 1) {
      if (ans == "") ans = (char)(i + 'a'); else ans = "Impossible";
    } else if (bin[i] == 2) {
      two++;
    }
  }
  if (two != 6) {
    ans = "Impossible";
  }
  cout << ans << endl;
  return 0;
}

int main() {
  for (;!cin.eof();cin>>ws) main2();
  return 0;
}