#include <algorithm>
#include <cstdio>
#include <iostream>
#include <map>
#include <cmath>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>
#include <stdlib.h>
#include <stdio.h>
#include <bitset>
using namespace std;
#define FOR(I,A,B) for(int I = (A); I < (B); ++I)
typedef long long ll;

int main()
{
  string abc = "abcdefghijklm";
  int cnt[13];
  FOR(i,0,13) cnt[i] = 0;
  string s;
  cin >> s;
  bool two = false;
  bool no = false;
  FOR(i,0,13) {
    if(s[i]>='a' && s[i]<='m') {
      cnt[s[i]-'a']++;
      if(cnt[s[i]-'a'] >= 2 && !two) two = true;
      else if(cnt[s[i]-'a'] >= 2 && two) {
        cout << "Impossible" << endl;
        return 0;
      }
    } else {
      cout << "Impossible" << endl;
      return 0;
    }  
  }
  if(two) {
    FOR(i,0,13) {
      if(cnt[i]==0) {
        cout << abc[i] << endl;
        return 0;
      }
    }
  } else {
    FOR(i,0,13) {
      cout << abc[i] << endl;
    }
  }
  return 0;
}