#include using namespace std; using lint = long long; using pint = pair; using plint = pair; struct fast_ios { fast_ios(){ cin.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(20); }; } fast_ios_; #define ALL(x) (x).begin(), (x).end() #define FOR(i, begin, end) for(int i=(begin),i##_end_=(end);i=i##_begin_;i--) #define REP(i, n) FOR(i,0,n) #define IREP(i, n) IFOR(i,0,n) template void ndarray(vector &vec, int len) { vec.resize(len); } template void ndarray(vector &vec, int len, Args... args) { vec.resize(len); for (auto &v : vec) ndarray(v, args...); } template void ndfill(V &x, const T &val) { x = val; } template void ndfill(vector &vec, const T &val) { for (auto &v : vec) ndfill(v, val); } template bool chmax(T &m, const T q) { if (m < q) {m = q; return true;} else return false; } template bool chmin(T &m, const T q) { if (m > q) {m = q; return true;} else return false; } template pair operator+(const pair &l, const pair &r) { return make_pair(l.first + r.first, l.second + r.second); } template pair operator-(const pair &l, const pair &r) { return make_pair(l.first - r.first, l.second - r.second); } template vector srtunq(vector vec) { sort(vec.begin(), vec.end()), vec.erase(unique(vec.begin(), vec.end()), vec.end()); return vec; } template istream &operator>>(istream &is, vector &vec) { for (auto &v : vec) is >> v; return is; } template ostream &operator<<(ostream &os, const vector &vec) { os << '['; for (auto v : vec) os << v << ','; os << ']'; return os; } #if __cplusplus >= 201703L template istream &operator>>(istream &is, tuple &tpl) { std::apply([&is](auto &&... args) { ((is >> args), ...);}, tpl); return is; } template ostream &operator<<(ostream &os, const tuple &tpl) { std::apply([&os](auto &&... args) { ((os << args << ','), ...);}, tpl); return os; } #endif template ostream &operator<<(ostream &os, const deque &vec) { os << "deq["; for (auto v : vec) os << v << ','; os << ']'; return os; } template ostream &operator<<(ostream &os, const set &vec) { os << '{'; for (auto v : vec) os << v << ','; os << '}'; return os; } template ostream &operator<<(ostream &os, const unordered_set &vec) { os << '{'; for (auto v : vec) os << v << ','; os << '}'; return os; } template ostream &operator<<(ostream &os, const multiset &vec) { os << '{'; for (auto v : vec) os << v << ','; os << '}'; return os; } template ostream &operator<<(ostream &os, const unordered_multiset &vec) { os << '{'; for (auto v : vec) os << v << ','; os << '}'; return os; } template ostream &operator<<(ostream &os, const pair &pa) { os << '(' << pa.first << ',' << pa.second << ')'; return os; } template ostream &operator<<(ostream &os, const map &mp) { os << '{'; for (auto v : mp) os << v.first << "=>" << v.second << ','; os << '}'; return os; } template ostream &operator<<(ostream &os, const unordered_map &mp) { os << '{'; for (auto v : mp) os << v.first << "=>" << v.second << ','; os << '}'; return os; } #ifdef HITONANODE_LOCAL #define dbg(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ") " << __FILE__ << endl #else #define dbg(x) #endif vector Solve(const string &S, const string &T) { vector reqlen; int tmp = 0; for (auto c : S) { while (tmp < T.length() and c != T[tmp]) tmp++; tmp++; reqlen.emplace_back(tmp); } return reqlen; } vector> buildNext(const string &T) { vector> nxt(26, vector(T.length() + 1, T.length() + 2)); IREP(i, T.length()) { REP(d, 26) nxt[d][i] = nxt[d][i + 1]; nxt[T[i] - 'a'][i] = i; } return nxt; } int main() { string S, T; cin >> S >> T; auto Srev = S, Trev = T; reverse(ALL(Srev)); reverse(ALL(Trev)); auto vb = Solve(Srev, Trev); reverse(vb.begin(), vb.end()); auto Snxt = buildNext(S), Tnxt = buildNext(T); int Scur = 0, Tcur = 0; string ret; dbg(Snxt[0]); dbg(vb); while (Scur < S.length()) { dbg((vector{Scur, Tcur})); int nxtc = -1; REP(d, 26) if (Snxt[d][Scur] < S.length()) { if (vb[Snxt[d][Scur]] + Tcur > T.length()) { nxtc = d; break; } } if (nxtc < 0) { puts("-1"); return 0; } ret += 'a' + nxtc; Scur = Snxt[nxtc][Scur] + 1; Tcur = Tnxt[nxtc][Tcur] + 1; } cout << ret << '\n'; }