#include "bits/stdc++.h"

#define rep(a,b) for(int a = 0;a < b;a++)
#define REP(i, x, n) for(int i = x; i < n; i++)
#define P(a) cout << a << endl
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
int dx[] = { 1, -1 , 0 , 0 };
int dy[] = { 0,  0,  1, -1 };
ll MOD = 1000000007;
unsigned long long str_to_int(std::string str) {
  unsigned long long ret;
  std::stringstream ss; ss << str;
  ss >> ret;
  return ret;
}

void solve(){
    string s;
    cin >> s;
    map<char,int> m;
    char c[26] = {'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z'};
    rep(i,s.length()){
        m[s[i]]++;
    }
    int two_count = 0;
    int extra = 0;
    rep(i,26){
        if(i >= 13 and m[c[i]] != 0){
            P("Impossible");
            return;
        }
        if(m[c[i]] == 2){
            if(i < 13) {
                two_count++;
            }else{
                extra++;
            }
        }else if(m[c[i]] > 2){
            extra++;
        }
    }
    if(extra != 0){
        P("Impossible");
        return;
    }
    if(two_count == 0){
        rep(i,13){
            if(m[c[i]] == 1) {
                P(c[i]);
            }
        }
        return;
    }else if(two_count == 1){
        rep(i,13){
            if(m[c[i]] == 0) {
                P(c[i]);
            }
        }
        return;
    }else{
        P("Impossible");
    }
}

int main() {
    solve();
    return 0;
}