// No.548 国士無双
// https://yukicoder.me/problems/no/548
//
#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

vector<char> solve(string &S);


int main() {
    cin.tie(nullptr);
    string S;
    cin >> S;

    vector<char> ans = solve(S);
    if (ans.empty())
        cout << "Impossible" << endl;
    else {
        for (auto a: ans)
            cout << a << endl;
    }
}


vector<char> solve(string &S) {
    vector<char> ans;
    vector<char> candidates {'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm'};

    for (char c: candidates) {
        string T = S + c;
        vector<int> count(13, 0);
        bool match = true;
        for (char t: T) {
            if ('a' <= t && t <= 'm')
                count[t-'a']++;
            else {
                match = false;
                break;
            }
        }
        if (*max_element(count.begin(), count.end()) > 2 || *min_element(count.begin(), count.end()) < 1)
            match = false;
        if (match)
            ans.push_back(c);
    }
    return ans;
}