#include <stdio.h>
#include <algorithm>
#include <deque>
#include <string>
#include <iostream>
using namespace std;
using ll = long long;

void solve();
int main() {
	solve();
#ifdef DBG
	while (true);
#endif
}

//587
void solve() {
	char s[14], c[26] = { 0 };
	int oc = 0, tc = 0;
	scanf("%s", s);
	for (int i = 0; i < 13; i++) {
		c[s[i] - 'a']++;
		if (c[s[i] - 'a'] == 1)
			oc++;
		else if (c[s[i] - 'a'] == 2)
			oc--, tc++;
		else if (3 <= c[s[i] - 'a'])
			tc--;
	}
	if (oc == 1 && tc == 6) {
		for (int i = 0; i < 26; i++)
			if (c[i] == 1)
				printf("%c\n", i + 'a');
	} else {
		printf("Impossible\n");
	}
}