#include <bits/stdc++.h>
using namespace std;
struct cww{cww(){ios::sync_with_stdio(false);cin.tie(0);}}star;
#define all(c) (c).begin(), (c).end()
#define rall(c) (c).rbegin(), (c).rend()
#define vv(type, c, m, n, i) vector<vector<type>> c(m, vector<type>(n, i))
#define rep(i,a,n) for(int i=(a), i##_len=(n); i<i##_len; ++i)
#define rrep(i,a,n) for(int i=(a), i##_len=(n); i>i##_len; --i)
#define len(x) ((int)(x).size())
#define mp make_pair
#define eb emplace_back
#define em emplace
#define fi first
#define se second
template<typename T> inline T min(vector<T>& v) {return *min_element(v.begin(), v.end());}
template<typename T> inline T max(vector<T>& v) {return *max_element(v.begin(), v.end());}
#define sum(a, b) accumulate(a, b)
#define chmax(a,b) if(a<b)a=b
#define chmin(a,b) if(a>b)a=b
template <class T> inline void print(T t){cout << t << "\n";}
template <class H, class... T> inline void print(H h, T... t){cout << h << " ";print(t...);}
typedef long long ll;
typedef long double ld;
typedef vector<int> vi;
typedef vector<double> vd;
typedef vector<long long> vll;
typedef vector<string> vs;
typedef vector<bool> vb;
typedef pair<int, int> pii;
string solve() {
	string s; cin >> s;
	map<char, int> m;
	for (char c : s) {
		++m[c];
	}
	if (len(m) != 7)
		return "Impossible";
	string ans;
	for (auto a: m) {
		if (a.se > 2)
			return "Impossible";
		if (a.se == 1)
			ans = a.fi;
	}
	return ans;
}
int main() {
	print(solve());
	return 0;
}