#include<iostream>
#include<string>
#include<cstdio>
#include<vector>
#include<cmath>
#include<algorithm>
#include<functional>
#include<iomanip>
#include<queue>
#include<ciso646>
#include<random>
#include<map>
#include<set>
#include<complex>
#include<bitset>
#include<stack>
#include<unordered_map>
#include<utility>
#include<tuple>
#include<cassert>
using namespace std;
typedef long long ll;
typedef unsigned int ui;
const ll mod = 1000000007;
const ll INF = (ll)1000000007 * 1000000007;
typedef pair<int, int> P;
#define stop char nyaa;cin>>nyaa;
#define rep(i,n) for(int i=0;i<n;i++)
#define per(i,n) for(int i=n-1;i>=0;i--)
#define Rep(i,sta,n) for(int i=sta;i<n;i++)
#define Per(i,sta,n) for(int i=n-1;i>=sta;i--)
#define rep1(i,n) for(int i=1;i<=n;i++)
#define per1(i,n) for(int i=n;i>=1;i--)
#define Rep1(i,sta,n) for(int i=sta;i<=n;i++)
typedef long double ld;
const ld eps = 1e-8;
const ld pi = acos(-1.0);
typedef pair<ll, ll> LP;
int dx[4]={1,-1,0,0};
int dy[4]={0,0,1,-1};

string S,T;
int n,m;
int s[100010];
int nxt1[100010][26],nxt2[100010][26];

void solve(){
    cin >> S;n=S.length();
    cin >> T;m=T.length();
    s[n]=m;
    rep(k,26){
        nxt1[n][k]=-1;
        nxt2[m][k]=-1;
    }
    per(i,n){
        rep(k,26){
            nxt1[i][k]=nxt1[i+1][k];
        }
        nxt1[i][S[i]-'a']=i;
    }
    per(i,m){
        rep(k,26){
            nxt2[i][k]=nxt2[i+1][k];
        }
        nxt2[i][T[i]-'a']=i;
    }
    per(i,n){
        int j=s[i+1];
        if(j<0) {
            s[i]=-1;
            continue;
        }
        while(true){
            j--;
            if(j<0) break;
            if(S[i]==T[j]){
                s[i]=j;
                break;
            }
        }
        if(j<0) s[i]=-1;
    }
    // rep(i,n+1){
    //     cout << s[i] << endl;
    // }
    vector<char> ans={};
    int pos1=0,pos2=0;
    while(true){
        //cout << pos1 << " " << pos2 << endl;
        bool flag=false;
        rep(k,26){
            int npos1=nxt1[pos1][k];
            if(npos1==-1) continue;
            int npos2=nxt2[pos2][k];
            if(npos2==-1){
                ans.push_back(S[npos1]);
                for(char c:ans){
                    cout << c << "";
                }
                cout << "" << endl;
                return;
            }
            if(npos2+1<=s[npos1+1]) continue;
            ans.push_back(S[npos1]);
            pos1=npos1+1;pos2=npos2+1;
            flag=true;
            break;
        }
        if(!flag) break;
    }
    cout << -1 << endl;
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << fixed << setprecision(50);
    solve();
}