#include <bits/stdc++.h>
using namespace std;
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) begin(v),end(v)
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }
using ll = long long;
using pii = pair<int, int>;
constexpr ll INF = 1ll<<30;
constexpr ll longINF = 1ll<<60;
constexpr ll MOD = 1000000007;
constexpr bool debug = false;
//---------------------------------//

int main() {
	string S;
	cin >> S;
	int cnt[13] = {};
	for (char c : S) ++cnt[c - 'a'];
	int one = 0, two = 0;
	REP(i, 13) {
		one += cnt[i] >= 1;
		two += cnt[i] >= 2;
	}
	char c = '~';
	if (one == 12 && two == 1) printf("%c\n", min_element(ALL(cnt)) - cnt + 'a');
	else if (one == 13 && two == 0) REP(i, 13) printf("%c\n", i + 'a');
	else puts("Impossible");
}