#include "bits/stdc++.h"
using namespace std;

#define DEBUG(x) cout<<#x<<": "<<x<<endl;
#define DEBUG_VEC(v) cout<<#v<<":";for(int i=0;i<v.size();i++) cout<<" "<<v[i]; cout<<endl

typedef long long ll;
#define vi vector<int>
#define vl vector<ll>
#define vii vector< vector<int> >
#define vll vector< vector<ll> >
#define vs vector<string>
#define pii pair<int,int>
#define pis pair<int,string>
#define psi pair<string,int>
#define pll pair<ll,ll>
const int inf = 1000000001;
const ll INF = 1e18 * 2;
#define MOD 1000000007
#define mod 1000000009
#define pi 3.14159265358979323846
#define Sp(p) cout<<setprecision(15)<< fixed<<p<<endl;
int dx[4] = { 1,0,-1,0 }, dy[4] = { 0,1,0,-1 };
int dx2[8] = { 1,1,0,-1,-1,-1,0,1 }, dy2[8] = { 0,1,1,1,0,-1,-1,-1 };


int main() {
	string s;
	cin >> s;
	int i, j;
	map<char, int> mp;
	set<char> st;
	for (i = 0; i < 13; i++) {
		st.insert(s[i]);
		mp[s[i]]++;
	}
	if (st.size() != 7) {
		cout << "Impossible" << endl;
		return 0;
	}
	vi ans;
	char res;
	for (auto itr = st.begin(); itr != st.end(); itr++) {
		ans.push_back(mp[*itr]);
		if (mp[*itr] == 1) {
			res = *itr;
		}
	}
	sort(ans.begin(), ans.end());
	vi check = { 1,2,2,2,2,2,2 };
	if (ans == check) {
		cout << res << endl;
	}
	else {
		cout << "Impossible" << endl;
	}
}