#include <iostream>
#include <vector>
#include <algorithm>
#include <string>
using namespace std;

int main()
{
	vector<int>alp(26);
	string s;
	cin >> s;

	for (int i = 0; i < s.size(); i++) {
		alp[s[i] - 'a']++;
	}

	int flag = 2;
	bool flag2 = false;
	int c;
	for (int i = 0; i < 13; i++) {
		if (alp[i] == 0) {
			if (flag==1) {
				flag = 0;
				break;
			}
			flag = 1;
			c = i;
		}
		else if (alp[i] > 2) {
			flag = 0;
			break;
		}
		else if (alp[i] == 2)flag2 = true;
	}

	if (flag == 1 && flag2) {
		cout << (char)(c + 'a') << endl;
	}
	else if (flag == 2) {
		for (int i = 0; i < 13; i++) {
			cout << (char)(i + 'a') << endl;
		}
	}
	else {
		cout << "Impossible" << endl;
	}

    return 0;
}