#include<bits/stdc++.h>
#define rep(i,n)for(int i=0;i<(n);i++)
using namespace std;

int cnt[26];
int main() {
	string s; cin >> s;
	for (char c : s) {
		cnt[c - 'a']++;
	}
	int zero = 0, two = 0;
	rep(i, 13) {
		if (cnt[i] == 0)zero++;
		else if (cnt[i] == 2)two++;
		else if (cnt[i] != 1) {
			puts("Impossible"); return 0;
		}
	}
	if (two > 1 || zero > 1) {
		puts("Impossible"); return 0;
	}
	if (zero) {
		rep(i, 26) {
			if (cnt[i] == 0) {
				printf("%c\n", i + 'a'); return 0;
			}
		}
	}
	rep(i, 13)printf("%c\n", i + 'a');
}