#include <bits/stdc++.h>
#define FOR(i,bg,ed) for(ll i=(bg);i<(ed);i++)
#define REP(i,n) FOR(i,0,n)
#define MOD 1000000007
//#define int long long
using namespace std;
typedef long long ll;
typedef vector<vector<ll>> mat;
const int INF = 1e9;

bool check(string str)
{
    bool two = false;
    for (char c='a'; c<='m'; c++) {
        int cnt = 0;
        REP(i,str.length()) if (c == str[i]) cnt++;
        if (cnt == 0) return false;
        else if (cnt == 1) continue;
        else if (cnt == 2) {
            if (two) return false;
            two = true;
        } else {
            return false;
        }
    }
    if (!two) return false;
    return true;
}

signed main()
{
    string S;
    cin >> S;

    bool find = false;
    for (char c='a'; c<='z'; c++) {
        //cout << "### " << c << " ###" << endl;
        if (check(S + c)) {
            cout << c << endl;
            find = true;
        }
    }

    if (!find) {
        cout << "Impossible" << endl;
    }
}