#include using namespace std; typedef long long ll; #define F first #define S second #define pii pair #define eb emplace_back #define all(v) v.begin(), v.end() #define rep(i, n) for (int i = 0; i < n; ++i) #define rep3(i, l, n) for (int i = l; i < n; ++i) #define chmax(a, b) a = (a >= b ? a : b) #define chmin(a, b) a = (a <= b ? a : b) #define out(a) cout << (a) << endl #define outa(a, n) rep(_, n) cout << a[_] << " "; cout << endl #define SZ(v) (int)v.size() #define inf (int)(1e9+7) #define abs(x) (x >= 0 ? x : -(x)) int main() { ios::sync_with_stdio(false); cin.tie(0); map mp; rep(i, 13) { char ch; cin >> ch; mp[ch]++; } vector v; for (auto e : mp) { if (e.S == 1) v.eb(e.F); else if (e.S > 2) { out("Impossible"); return 0; }} if (SZ(v) != 1 && SZ(mp) != 7) out("Impossible"); else if (SZ(v) == 1) out(v[0]); }