#include <iostream>
#include <algorithm>
using namespace std;
int main(){
    string s;cin>>s;sort(s.begin(),s.end());s.erase(unique(s.begin(),s.end()),s.end());
    if(s.size() == 13){
        for(char i = 'a'; 'm' >= i; i++){
            cout << i << endl;
        }
    }else if(s.size() == 12){
        for(int i = 0; 13 > i; i++){
            if(s[i] != 'a'+i){
                cout << (char)('a'+i) << endl;
                return 0;
            }
        }
    }else{
        cout << "Impossible" << endl;
    }
}