// No.587 七対子
// https://yukicoder.me/problems/no/587
//

#include <iostream>
#include <string>
#include <unordered_map>
using namespace std;

string solve(string &S);


int main() {
    cin.tie(0);
    string S;
    cin >> S;

    string ans = solve(S);
    cout << ans << endl;
}

string solve(string &S) {
    unordered_map<char, int> char_count;
    for (char s: S)
        char_count[s]++;

    string ans = "";
    for (auto c: char_count) {
        if (c.second > 2) {
            ans = "Impossible";
            break;
        } else if (c.second == 1) {
            if (ans != "") {
                ans = "Impossible";
                break;
            }
            ans += c.first;
        }
    }
    return ans;
}