#include "bits/stdc++.h"
using namespace std;
#define fastcin {\
    cin.tie(0);\
    ios::sync_with_stdio(false);\
}
#define rep(i, a, b) for(int i = a; i < b; i++)
#define rrep(i, a, b) for(int i = a; i >= b; i--)
#define fore(i, a) for(auto &i:a)
#define print(x) cout << x << "\n"
#define SORT(a, n) sort(a, a+n);
#define REVERSE(a,n) reverse(a,a+n);
#define VSORT(v) sort(v.begin(), v.end());
#define VREVERSE(v) reverse(v.begin(), v.end());
#define MOD 1000000007
#define yes "YES"
#define no "NO"
typedef long long ll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<ll> vll;

int main() {
    fastcin;
    int cl[13] = {};
    bool f = false;
    char c;
    string a;
    rep(i, 0, 13) {
        cin >> c;
        if(c > 'm' || (f &&(cl[c-'a']==1))) {
            a = "Impossible";
        } else {
            if(cl[c-'a']==1) f = true; 
            cl[c-'a']++;
        }
    }
    if(a.size()==0) {
        if(f) {
            rep(i, 0, 13) {
                if(cl[i]==0) {
                    a = 'a' + i;
                    break;
                }
            }
        } else {
            rep(i, 0, 13) a.push_back('a'+i);
        }
        rep(i, 0, a.size()) print(a[i]);
    } else print(a);
    
    return 0;
}