#include <algorithm>
#include <cfloat>
#include <climits>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <functional>
#include <iostream>
#include <map>
#include <memory>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <utility>
#include <vector>

using namespace std;

typedef long long ll;

#define sz size()
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define all(c) (c).begin(), (c).end()
#define rep(i,a,b) for(ll i=(a);i<(b);++i)
#define per(i,a,b) for(ll i=(b-1);i>=(a);--i)
#define clr(a, b) memset((a), (b) ,sizeof(a))
#define ctos(c) string(1,c)
#define print(x) cout<<#x<<" = "<<x<<endl;

#define MOD 1000000007

int main() {
  string s;
  cin>>s;
  map<char,ll> ma;
  rep(i,0,s.sz){
    ma[s[i]]++;
  }
  map<char,ll>::iterator itr = ma.begin();
  ll d[3];
  clr(d,0);
  while(itr!=ma.end()){
    char a = (*itr).fi;
    ll b = (*itr).se;
    if(b>2){
      cout << "Impossible" << endl;
      return 0;
    }
    d[b]++;
    itr++;
  }
  if(d[2]==6&&d[1]==1){
    map<char,ll>::iterator itr1 = ma.begin();
    while(itr1!=ma.end()){
      char a = (*itr1).fi;
      ll b = (*itr1).se;
      if(b==1){
        cout << a << endl;
        return 0;
      }
      itr1++;
    }
  }
  cout << "Impossible" << endl;
	return 0;
}