#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
using namespace std;
int main(){
	string S;
	cin >> S;
	bool ok = false;
	for (int i = 0; i < 13; i++){
		char c = 'a' + i;
		string T = S + c;
		vector<int> cnt(13, 0);
		for (int j = 0; j < 14; j++){
			cnt[T[j] - 'a']++;
		}
		sort(cnt.begin(), cnt.end());
		if (cnt[12] != 0){
			cout << c << endl;
			ok = true;
		}
	}
	if (!ok){
		cout << "Impossible" << endl;
	}
}