#define _USE_MATH_DEFINES
#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
#include<string>
#include<iostream>
#include<iostream>
#include<cctype>
#include<cstdio>
#include<vector>
#include<stack>
#include<queue>
#include <algorithm>
#include<math.h>
#include<set>
#include<map>
#include <sstream>
#include<iomanip>
#include <ctype.h>
using namespace std;

//#include<bits/stdc++.h>

int main() {
	bool f[20] = {};
	string p;
	cin >> p;
	sort(p.begin(), p.end());
	vector<char>r;
	set<char>a;

	for (int i = 0; i < p.size(); i ++) {
		a.insert(p[i]);// cout << f[i];
		if (f[i])continue;
		for (int j = i + 1; j <= p.size(); j++) {
			if (p[i] == p[j]) {
				f[j] = 1; f[i] = 1;
				break;
			}
		}
		
	}
	for (int i = 0; i < p.size(); i++) {
		if (!f[i])r.push_back(p[i]); 
	}

	if(r.size()>1||a.size()!=7)cout << "Impossible" << endl;
	else cout << r[0] << endl;

	return 0;
}