#include "bits/stdc++.h"

using namespace std;

using ll = long long int;
using ld = long double;

using vi = vector<int>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using vl = vector<ll>;
using vvl = vector<vl>;
using vvvl = vector<vvl>;
using vd = vector<double>;
using vvd = vector<vd>;
using vs = vector<string>;
using vb = vector<bool>;
using vvb = vector<vb>;

const int INF = (1 << 30) - 1;
const ll INF64 = ((ll)1 << 62) - 1;
const double PI = 3.1415926535897932384626433832795;

const int dx[] = { -1, 0, 1, 0 };
const int dy[] = { 0, 1, 0, -1 };

int gcd(int x, int y) { return y ? gcd(y, x % y) : x; }
ll gcd(ll x, ll y) { return y ? gcd(y, x % y) : x; }
int lcm(int x, int y) { return x / gcd(x, y) * y; }
ll lcm(ll x, ll y) { return x / gcd(x, y) * y; }

bool check(string s) {
	map<char, int> m;
	for (auto c : s) {
		m[c]++;
	}

	vi v;
	for (int i = 0; i <= 12; i++) {
		if (m['a' + i]) {
			v.push_back(m['a' + i]);
		}
	}
	sort(v.begin(), v.end());

	if (v.size() != 13) {
		return false;
	}
	for (int i = 0; i < 12; i++) {
		if (v[i] != 1) {
			return false;
		}
	}

	if (v[12] != 2) {
		return false;
	}

	return true;
}

int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);

	string s;
	cin >> s;

	string res = "";
	for (int i = 0; i <= 12; i++) {
		char c = 'a' + i;
		if (check(s + c)) {
			res += c;
		}
	}

	if (res.size() == 0) {
		cout << "Impossible" << endl;
	} else {
		for (auto c : res) {
			cout << c << endl;
		}
	}
	return 0;
}