#include <iostream>
#include <string>
#include <vector>

using namespace std;

int main() {
	string s;
	cin >> s;

	vector<vector<bool>> alpha(3, vector<bool>(13, false));
	alpha[0].assign(13, true);

	int n0 = 13;
	int n1 = 0;
	int n2 = 0;

	bool ok = true;
	for (auto c : s) {
		int idx = c - 'a';
		if (alpha[2][idx]) {
			ok = false;
			break;
		} else if (alpha[1][idx]) {
			alpha[1][idx] = false;
			alpha[2][idx] = true;
			n1--;
			n2++;
		} else if (alpha[0][idx]) {
			alpha[0][idx] = false;
			alpha[1][idx] = true;
			n0--;
			n1++;
		} else {
			ok = false;
			break;
		}
	}

	if (n2 > 1 || n0 > 1) {
		ok = false;
	}

	for (auto v : alpha) {
		for (auto b : v) {
			cerr << (b ? 'O' : '-');
		}
		cerr << endl;
	}

	if (ok) {
		int idx = n0 == 1 ? 0 : 1;
		for (int i = 0; i < alpha[idx].size(); i++) {
			if (alpha[idx][i]) {
				cout << (char)('a' + i) << endl;
			}
		}
	} else {
		cout << "Impossible" << endl;
	}
	return 0;
}