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

int main(){
    map <char, int> mp;
    string str;
    string abc = "abcdefghijklm";
    int cnt = 0;
    char daburi = 0, tmp;

    cin >> str;
    sort(str.begin(), str.end());
    for(int i = 0; i < 13; i++){
        if(str[i] != abc[i]){
            tmp = abc[i];
            break;
        }
    }

    for(int i = 0; i < str.size(); i++){
        mp[str[i]]++;
    }
    for(auto itr = mp.begin(); itr != mp.end(); itr++){
        if(itr->second != 0){
            cnt++;
        }
        if(itr->second == 2){
            daburi = itr->first;
        }
    }

    if(daburi != 0 && cnt == 12){
        cout << tmp << endl;
    }else if(daburi == 0 && cnt == 13){
        for(auto itr = mp.begin(); itr != mp.end(); itr++){
            cout << itr->first << endl;
        }
    }else{
        cout << "Impossible" << endl;
    }

    return 0;
}