import std.conv, std.functional, std.range, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.bitmanip, std.complex, std.container, std.math, std.mathspecial, std.numeric, std.regex, std.typecons;
import core.bitop;

class EOFException : Throwable { this() { super("EOF"); } }
string[] tokens;
string readToken() { for (; tokens.empty; ) { if (stdin.eof) { throw new EOFException; } tokens = readln.split; } auto token = tokens.front; tokens.popFront; return token; }
int readInt() { return readToken.to!int; }
long readLong() { return readToken.to!long; }
real readReal() { return readToken.to!real; }

bool chmin(T)(ref T t, in T f) { if (t > f) { t = f; return true; } else { return false; } }
bool chmax(T)(ref T t, in T f) { if (t < f) { t = f; return true; } else { return false; } }

int binarySearch(alias pred, T)(in T[] as) { int lo = -1, hi = cast(int)(as.length); for (; lo + 1 < hi; ) { const mid = (lo + hi) >> 1; (unaryFun!pred(as[mid]) ? hi : lo) = mid; } return hi; }
int lowerBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a >= val)); }
int upperBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a > val)); }


enum A = 26;

int[][] getNxt(string s) {
  const m = cast(int)(s.length);
  auto nxt = new int[][](A, m + 1);
  foreach (a; 0 .. A) {
    nxt[a][m] = m;
    foreach_reverse (i; 0 .. m) {
      nxt[a][i] = (s[i] - 'a' == a) ? i : nxt[a][i + 1];
    }
  }
  return nxt;
}

void main() {
  try {
    for (; ; ) {
      const S = readToken();
      const T = readToken();
      const M = cast(int)(S.length);
      const N = cast(int)(T.length);
      
      const nxtS = getNxt(S);
      const nxtT = getNxt(T);
      
      auto rs = new int[M + 1];
      rs[M] = N;
      foreach_reverse (i; 0 .. M) {
        rs[i] = max(rs[i + 1] - 1, -1);
        for (; rs[i] >= 0 && S[i] != T[rs[i]]; --rs[i]) {}
      }
      debug {
        writeln("rs = ", rs);
      }
      
      if (rs[0] < 0) {
        string ans;
        int i, j;
        for (; ; ) {
          if (j > N) {
            break;
          }
          foreach (a; 0 .. A) {
            if (nxtS[a][i] < M) {
              const ii = nxtS[a][i] + 1;
              const jj = nxtT[a][j] + 1;
              if (rs[ii] < jj) {
                ans ~= cast(char)('a' + a);
                i = ii;
                j = jj;
                goto found;
              }
            }
          }
          assert(false);
         found:
        }
        writeln(ans);
      } else {
        writeln("-1");
      }
    }
  } catch (EOFException e) {
  }
}