#define _CRT_SECURE_NO_WARNINGS

#include <iostream>
#include <string>
#include <vector>
#include <cmath>
#include <fstream>
#include <set>
#include <utility>
#include <algorithm>
#include <queue>
#include <stack>
#include <deque>
#include <numeric>
#include <sstream>
#include <list>
#include <map>

#define rep(i,p,n) for(int i=(int)p;i<(int)n;i++)
#define repp(i,p,n) for(int i=(int)p;i>=(int)n;i--)
#define Sort(x) sort(x.begin(),x.end());
#define ll long long 
#define vi vector<int>
#define vvi vector<vector<int>>
#define vvvi <vector<vector<vector<int>>> 
#define vc vector<char> 
#define vvc vector<vector<char>>
#define vvvc vector<vector<vector<char>>> 
#define INF 2000000000

using namespace std;

int main() {
	string s;
	int c[26] = {0};

	cin >> s;
	rep(i, 0, s.length()) {
		c[s[i] - 'a']++;
	}

	int count = 0;
	rep(i, 0, 26) {
		if (c[i] == 2) count ++;
	}

	if (count == 6) {
		rep(i, 0, 26) {
			if (c[i] == 1) {
				cout << (char)('a' + i) << endl;
				break;
			}
		}
	}
	else cout << "Impossible" << endl;

	return 0;
}