#include <cmath>
#include <vector>
#include <list>
#include <map>
#include <set>
#include <functional>
#include <queue>
#include <iostream>
#include <string.h>
#include <iomanip>
#include <algorithm>
#include <functional>
#include <cstdint>
#include <climits>
#include <unordered_set>
#include <sstream>
#include <stack>

using namespace std;

typedef long long int ll;
typedef pair<int,int> pii;
typedef tuple<int,int,int> t3;

int main()
{
    set<char> u;
    const string key = "abcdefghijklm";
    for(char c : key)
    {
        u.insert(c);
    }
    string s;
    cin >> s;
    map<char,int> m;
    for(char c : s)
    {
        if(u.find(c) != u.end())
        {
            m[c]++;
        }
    }
    const string err = "Impossible";
    if(m.size() <= 11)
    {
        cout << err << endl;
        return 0;
    }
    if(m.size() == 12)
    {
        for(auto c : u)
        {
            if(m[c] == 0)
            {
                cout << c << endl;
                return 0;
            }
        }
        return 0;
    }
    if(m.size() == 13)
    {
        for(auto c : u)
        {
            cout << c << endl;
        }
        return 0;
    }
    else
    {
        cout << err << endl;
        return 0;
    }
}