#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 * 4;
#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;
	sort(s.begin(), s.end());
	char pre = s[0];
	int cnt = 1;
	vi d;
	char ans = '0';
	for (int i = 1; i < 13; i++) {
		if (pre == s[i]) {
			cnt++;
		}
		else {
			if (cnt == 1) {
				ans = pre;
			}
			d.push_back(cnt);
			pre = s[i];
			cnt = 1;
		}
	}
	d.push_back(cnt);
	sort(d.begin(), d.end());
	//DEBUG_VEC(d);
	vi a = { 1,2,2,2,2,2,2 };
	if (a == d) {
		cout << ans << endl;
	}
	else {
		cout << "Impossible" << endl;
	}

}