#include using namespace std; using int64 = long long; // const int mod = 1e9 + 7; const int mod = 998244353; const int64 infll = (1LL << 62) - 1; const int inf = (1 << 30) - 1; struct IoSetup { IoSetup() { cin.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(10); cerr << fixed << setprecision(10); } } iosetup; template< typename T1, typename T2 > ostream &operator<<(ostream &os, const pair< T1, T2 > &p) { os << p.first << " " << p.second; return os; } template< typename T1, typename T2 > istream &operator>>(istream &is, pair< T1, T2 > &p) { is >> p.first >> p.second; return is; } template< typename T > ostream &operator<<(ostream &os, const vector< T > &v) { for(int i = 0; i < (int) v.size(); i++) { os << v[i] << (i + 1 != v.size() ? " " : ""); } return os; } template< typename T > istream &operator>>(istream &is, vector< T > &v) { for(T &in : v) is >> in; return is; } template< typename T1, typename T2 > inline bool chmax(T1 &a, T2 b) { return a < b && (a = b, true); } template< typename T1, typename T2 > inline bool chmin(T1 &a, T2 b) { return a > b && (a = b, true); } template< typename T = int64 > vector< T > make_v(size_t a) { return vector< T >(a); } template< typename T, typename... Ts > auto make_v(size_t a, Ts... ts) { return vector< decltype(make_v< T >(ts...)) >(a, make_v< T >(ts...)); } template< typename T, typename V > typename enable_if< is_class< T >::value == 0 >::type fill_v(T &t, const V &v) { t = v; } template< typename T, typename V > typename enable_if< is_class< T >::value != 0 >::type fill_v(T &t, const V &v) { for(auto &e : t) fill_v(e, v); } template< typename F > struct FixPoint : F { FixPoint(F &&f) : F(forward< F >(f)) {} template< typename... Args > decltype(auto) operator()(Args &&... args) const { return F::operator()(*this, forward< Args >(args)...); } }; template< typename F > inline decltype(auto) MFP(F &&f) { return FixPoint< F >{forward< F >(f)}; } int main() { string S, T; cin >> S >> T; int N = (int) S.size(); int M = (int) T.size(); vector< vector< int > > appearS(N + 1), appearT(M + 1); { vector< int > buf(26, inf); appearS[N] = buf; for(int i = N - 1; i >= 0; i--) { buf[S[i] - 'a'] = i + 1; appearS[i] = buf; } } { vector< int > buf(26, inf); appearT[M] = buf; for(int i = M - 1; i >= 0; i--) { buf[T[i] - 'a'] = i + 1; appearT[i] = buf; } } { int ptr = 0; for(auto &c : S) { ptr = appearT[ptr][c - 'a']; if(ptr == inf) break; } if(ptr <= M) { cout << -1 << "\n"; return 0; } } vector< int > last(N + 1); { int ptr = N - 1; last[N] = M; for(int i = M - 1; i >= 0; i--) { if(ptr >= 0 && S[ptr] == T[i]) { last[ptr] = i + 1; --ptr; } } } string ans; int Spos = 0, Tpos = 0; for(; Tpos != inf;) { for(int i = 0; i < 26; i++) { int Snxt = appearS[Spos][i]; int Tnxt = appearT[Tpos][i]; if(Snxt == inf) continue; if(last[Snxt] <= Tnxt) { Spos = Snxt; Tpos = Tnxt; ans += (char) (i + 'a'); break; } } } cout << ans << "\n"; }