#include <iostream>
#include <algorithm>
#include <string>
#include <vector>
#include <cmath>
#include <map>
#include <queue>
#include <iomanip>
#include <set>
#include <tuple>
#define mkp make_pair
#define mkt make_tuple
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define all(v) v.begin(),v.end()
using namespace std;
typedef long long ll;
const ll MOD=1e9+7;
template<class T> void chmin(T &a,const T &b){if(a>b) a=b;}
template<class T> void chmax(T &a,const T &b){if(a<b) a=b;}

int main(){
  cin.tie(0);
  ios::sync_with_stdio(false);

  string S,T;
  cin>>S;
  cin>>T;

  int N=S.size();
  int M=T.size();
  vector<vector<int>> back(M+1,vector<int> (26,-1));
  for(int i=0;i<=M;i++){
    for(int j=0;j<26;j++){
      if(i-1>=0) back[i][j]=back[i-1][j];
    }
    if(i<M) back[i][T[i]-'a']=i;
  }
  vector<int> dp(N+1,-1);
  dp[N]=M;
  for(int i=N-1;i>=0;i--){
    if(dp[i+1]==-1) continue;
    if(dp[i+1]==0){
      dp[i]=-1;
      continue;
    }
    
    int pos=dp[i+1]-1;
    dp[i]=back[pos][S[i]-'a'];
  }
  
  if(dp[0]!=-1){
    cout<<-1<<endl;
    return 0;
  }

  vector<vector<int>> nxt(N+1,vector<int> (26,N));
  for(int i=N-1;i>=0;i--){
    for(int j=0;j<26;j++){
      nxt[i][j]=nxt[i+1][j];
    }
    nxt[i][S[i]-'a']=i;
  }

  string ans="";
  int now=0;
  int tar=0;
  while(now<N){
    int nexchar=0;
    for(int k=0;k<26;k++){
      int nex=nxt[now][k];
      if(nex==N) continue;
      if(dp[nex]<tar){
        ans+=char('a'+k);
        nexchar=k;
        break;
      }
    }
    
    while(tar<M&&T[tar]-'a'!=nexchar) tar++;
    if(tar==M) break;

    now=nxt[now][nexchar]+1;
    tar++;
  }

  cout<<ans<<endl;

  return 0;
}