#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll = long long;
using ld = long double;

string S;
map<char, int> mp;

int main() {
  cin >> S;
  int N = S.size();
  for (int i = 0; i < N; i++) mp[S[i]]++;
  if (mp.size() == 7) {
    for (auto p: mp) {
      if (p.second == 1) {
        cout << p.first << endl;
        return 0;
      }
    }
  } else {
    cout << "Impossible" << endl;
  }
  return 0;
}