#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>
#include <cstring>
#include <deque>
using namespace std;
#define FOR(I,A,B) for(int I = (A); I < (B); ++I)
#define CLR(mat) memset(mat, 0, sizeof(mat))
typedef long long ll;
int main()
{
  ios::sync_with_stdio(false);
  cin.tie(0);
  int cnt[26]; CLR(cnt);
  string s; cin >> s;
  FOR(i,0,13) cnt[s[i] - 'a']++;
  int cnt1 = 0, cnt2 = 0;
  char c;
  FOR(i,0,26) {
    if(cnt[i] == 2) cnt2++;
    if(cnt[i] == 1) cnt1++, c = 'a' + i;
  }
  if(cnt1 == 1 && cnt2 == 6) {
    cout << c << endl;
  } else {
    cout << "Impossible" << endl;
  }
  return 0;
}