#include <bits/stdc++.h>
using namespace std;
typedef int ll;
#define REP(i,n) FOR(i,0,n)
#define FOR(i,a,b) for(ll i=a;i<b;i++)
#define PB push_back
#define LB lower_bound
#define UB upper_bound
#define PQ priority_queue
#define UM unordered_map
#define ALL(a) (a).begin(),(a).end()
typedef vector<ll> vi;
typedef vector<vector<ll>> vvi;
const ll INF = (1ll << 30);
typedef pair<ll,ll> pii;
struct Edge{ ll s,t,c; };
typedef vector<vector<Edge>> Graph;
typedef vector<pii> vpii;

int main() {
  string S; cin>>S;
  UM<char,ll> um;
  for(char c:S) um[c]++;
  UM<ll,ll> um2;
  for(auto p:um) um2[p.second]++;
  if(um2[1]!=1||um2[2]!=6) {
    cout<<"Impossible"<<endl;
    return 0;
  }
  for(auto p:um) {
    if(p.second==1) {
      cout<<p.first<<endl;
    }
  }

}