#include <iostream>
#include <algorithm>
#include <cstring>
#include <string>
#include <vector>
#include <queue>
#include <deque>
#include <cmath>

#define AS(a) (sizeof(a)/sizeof(a[0]))
using namespace std;
long long int MOD = 1000000007;
long long int INF = 1000000007;


int main() {
  string s;
  cin >> s;
  int cou[26];
  for(int i = 0; i < 26; i++) {
    cou[i] = 0;
  }
  for(int i = 0; i < s.length(); i++) {
    cou[s[i] - 'a']++;
  }
  int id = -1;

  for(int i = 0; i < 13; i++) {
    if(cou[i] == 0 && id == -1) {
      id = i;
    } else if(cou[i] == 0 && id != -1) {
      id = -2;
    }
  }
  if(id == -2) {
    cout << "Impossible" << endl;
  }
  else if(id == -1) {
    for(int i = 0; i < 13; i++) {
      cout << (char)('a' + i) << endl;
    }
  }
  else {
    cout << (char)('a' + id) << endl;
  }

}