#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
#include<cstdio>
#include<string>
#include<algorithm>
#include<cmath>
using namespace std;

int main() {
	string S;
	int table[13] = {};
	cin >> S;
	int len = S.length();
	for (int i = 0;i < len;i++) {
		for (int j = 0;j < 13; j++) {
			if (S[i] == 'a' + j) {
				table[j]++;
			}
		}
	}

	int zer = 0;
	for (int j = 0; j < 13;j++) {
		if (table[j] == 0) zer++;
	}
	if (zer >= 2) {
		cout << "Impossible" << endl;
		return 0;
	}

	for (int j = 0; j < 13;j++) {
		if (table[0] == 0) {
			cout << "a" << endl; return 0;
		}
		if (table[1] == 0) {
			cout << "b" << endl;return 0;
		}
		if (table[2] == 0) {
			cout << "c" << endl;return 0;
		}
		if (table[3] == 0) {
			cout << "d" << endl;return 0;
		}
		if (table[4] == 0) {
			cout << "e" << endl;return 0;
		}
		if (table[5] == 0) { cout << "f" << endl;return 0; }
		if (table[6] == 0) { cout << "g" << endl;return 0; }
		if (table[7] == 0) {cout << "h" << endl;return 0;}
		if (table[8] == 0) { cout << "i" << endl;return 0; }
		if (table[9] == 0) { cout << "j" << endl;return 0; }
		if (table[10] == 0) { cout << "k" << endl;return 0; }
		if (table[11] == 0) { cout << "l" << endl;return 0; }
		if (table[12] == 0) { cout << "m" << endl;return 0; }
	}

	

	if (table[0] == 1) cout << "a" << endl;
	if (table[1] == 1) cout << "b" << endl;
	if (table[2] == 1) cout << "c" << endl;
	if (table[3] == 1) cout << "d" << endl;
	if (table[4] == 1) cout << "e" << endl;
	if (table[5] == 1) cout << "f" << endl;
	if (table[6] == 1) cout << "g" << endl;
	if (table[7] == 1) cout << "h" << endl;
	if (table[8] == 1) cout << "i" << endl;
	if (table[9] == 1) cout << "j" << endl;
	if (table[10] == 1) cout << "k" << endl;
	if (table[11] == 1) cout << "l" << endl;
	if (table[12] == 1) cout << "m" << endl;


	return 0;
}