#include<bits/stdc++.h>

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";
}