#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<(n);++i)
#define all(a) (a).begin(),(a).end()
using namespace std;
typedef long long ll;

int main(){
  ios::sync_with_stdio(false);
  cin.tie(0);
  string S;
  cin >> S;
  
  sort(all(S));
  string T = S;
  auto result = unique(all(S));
  S.erase(result, S.end());
  
  vector<char> ans = {'a','b','c','d','e','f','g','h','i','j','k','l','m'};
  
  if(T.size() == S.size() + 1){
  	rep(i,13){
  		if(count(all(S),ans[i]) == 0){
  			cout << ans[i] << endl;
  			return 0;
  		}
  	}
  }
  else if(T.size() == S.size()){
  	rep(i,13){
  		cout << ans[i] << endl;
  	}
  }
  else cout << "Impossible" << endl;
  
  return 0;
}