#include "bits/stdc++.h"
using namespace std;
#define rep(i,n) for(int (i)=0;(i)<(int)(n);++(i))
#define rer(i,l,u) for(int (i)=(int)(l);(i)<=(int)(u);++(i))
#define reu(i,l,u) for(int (i)=(int)(l);(i)<(int)(u);++(i))
static const int INF = 0x3f3f3f3f; static const long long INFL = 0x3f3f3f3f3f3f3f3fLL;
typedef vector<int> vi; typedef pair<int, int> pii; typedef vector<pair<int, int> > vpii; typedef long long ll;
template<typename T, typename U> static void amin(T &x, U y) { if (y < x) x = y; }
template<typename T, typename U> static void amax(T &x, U y) { if (x < y) x = y; }

int main() {
	string S;
	while (cin >> S) {
		bool imp = true;
		for (char a : "abcdefghijklm") if (a) {
			string t = S + a;
			map<int, int> cnt;
			for (char c : t)
				++ cnt[c];
			map<int, int> aa;
			for (char a : "abcdefghijklm") if (a)
				++ aa[cnt[a]];
			if (aa[1] == 12 && aa[2] == 1) {
				imp = false;
				cout << a << endl;
			}
		}
		if (imp) puts("Impossible");
	}
	return 0;
}