#include <bits/stdc++.h>
using namespace std;
bool solve(string x) {
	vector<int> c(13);
	for(int i = 0; i < x.size(); i++) {
		if(x[i] >= 'n') return false;
		c[x[i] - 97]++;
	}
	sort(c.begin(), c.end());
	return c[0] == 1 && c[11] == 1;
}
string s;
int main() {
	cin >> s;
	bool flag = false;
	for(char c = 'a'; c <= 'm'; c++) {
		string t = s + c;
		if(solve(t)) flag = true, cout << c << endl;
	}
	if(!flag) cout << "Impossible" << endl;
	return 0;
}