#include <iostream>
#include <algorithm>
using namespace std;

int main(){
	string s;
	cin >> s;
	int a[26]{};
	for(char c:s) a[c - 'a']++;
	bool f = false;
	for(char c = 'n'; c <= 'z'; c++) f |= a[c - 'a'];
	if(f){
		cout << "Impossible" << endl;
		return 0;
	}
	bool flag = true;
	for(char c = 'a'; c <= 'm'; c++){
		a[c - 'a']++;
		bool f = true;
		for(int i = 0; i < 13; i++) f &= !!a[i];
		if(f && count(a, a + 13, 2) == 1 && count(a, a + 13, 1) == 12){
			cout << c << endl;
			flag = false;
		}
		a[c - 'a']--;
	}
	if(flag) cout << "Impossible" << endl;
}