#include using namespace std; #ifdef DEBUG_ #include #else #define dump(...) #endif #define FastIO cin.tie(nullptr), ios_base::sync_with_stdio(false); #define rep(i, n) for (int i = 0; (int)i < n; ++i) #define repa(i, a, n) for (int i = a; (int)i < n; ++i) #define rrep(i, n) for (int i = n; (int)i >= 0; --i) #define rrepa(i, a, n) for (int i = a; (int)i >= n; --i) #define EACH(x, a) for (auto& x : a) #define output(msg) cout << (msg) << '\n' #define die(msg) \ do { \ cout << msg << endl; \ exit(0); \ } while (0) template void read(vector& v); template void read(array& a); template void read(T& x) { cin >> x; } void read(double& d) { string t; read(t); d = stod(t); } void read(long double& d) { string t; read(t); d = stold(t); } template void read(H& h, T&... t) { read(h); read(t...); } template void read(vector& x) { EACH(a, x) read(a); } template void read(array& x) { EACH(a, x) read(a); } template bool chmax(T& a, const T& b) { return ((a < b) ? (a = b, true) : (false)); } template bool chmin(T& a, const T& b) { return ((a > b) ? (a = b, true) : false); } using llint = long long int; int main() { FastIO; string s; read(s); map mp; for (auto ch : s) { mp[ch]++; } if (mp.size() != 7) die("Impossible"); int cnt{}; char adding{}; for (auto key : mp) { if (key.second == 1) { cnt++; adding = key.first; } else if (key.second == 2) { continue; } else { die("Impossible"); } } if (cnt != 1) output("Impossible"); else output(adding); }