#include<algorithm>
#include<complex>
#include<ctype.h>
#include<iomanip>
#include<iostream>
#include<fstream>
#include<map>
#include<math.h>
#include<numeric>
#include<queue>
#include<set>
#include<stack>
#include<stdio.h>
#include<string>
#include<string>
#include<vector>

using namespace std;
typedef long long ll;

#define FOR(i,a,b) for(ll i=(a);i<(b);++i)
#define ALL(v) (v).begin(), (v).end()
#define p(s) cout<<(s)<<endl
#define p2(s, t) cout << (s) << " " << (t) << endl
#define br() p("")
#define pn(s) cout << (#s) << " " << (s) << endl
#define p_yes() p("Yes")
#define p_no() p("No")

const ll mod = 1e9 + 7;
const ll inf = 1e18;

string alphabets = "abcdefghijklm";
vector<string> kokushi_list;

bool is_kokushi(string s){
    for(string kokushi : kokushi_list){
        if(s==kokushi){
            return true;
        }
    }
    return false;
}

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);

    for(char c : alphabets){
        string t = alphabets + c;
        sort(ALL(t));
        kokushi_list.push_back(t);
    }

    // input
    string s;
    cin >> s;
    sort(ALL(s));

    if(s==alphabets){
        // p("すべてが1回ずつ");
        for(char c : alphabets){
            p(c);
        }
        return 0;
    }

    // 文字を加えてみて国士無双になるか見てみる
    for(char c : alphabets){
        string t = s + c;
        sort(ALL(t));

        if(is_kokushi(t)){
            p(c);
            return 0;
        }
    }

    p("Impossible");

    return 0;
}