//Let's join Kaede Takagaki Fan Club !!
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
typedef long long ll;
typedef pair<int,int> P;
typedef pair<int,P> P1;
typedef pair<P,P> P2;
#define pu push
#define pb push_back
#define mp make_pair
#define eps 1e-7
#define INF 1000000000
#define fi first
#define sc second
#define rep(i,x) for(int i=0;i<x;i++)
#define repn(i,x) for(int i=1;i<=x;i++)
#define SORT(x) sort(x.begin(),x.end())
#define ERASE(x) x.erase(unique(x.begin(),x.end()),x.end())
#define POSL(x,v) (lower_bound(x.begin(),x.end(),v)-x.begin())
#define POSU(x,v) (upper_bound(x.begin(),x.end(),v)-x.begin())
#define all(x) x.begin(),x.end()
template<class T>
void dmp(T a){
	rep(i,a.size()) cout << a[i] << " ";
	cout << endl;
}
template<class T>
bool chmax(T&a, T b){
	if(a < b){
		a = b;
		return 1;
	}
	return 0;
}
template<class T>
bool chmin(T&a, T b){
	if(a > b){
		a = b;
		return 1;
	}
	return 0;
}
template<class T>
void g(T &a){
	cin >> a;
}
template<class T>
void o(const T &a,bool space=false){
	cout << a << (space?' ':'\n');
}
//ios::sync_with_stdio(false);
const ll mod = 998244353;
template<class T>
void add(T&a,T b){
	a+=b;
	if(a >= mod) a-=mod;
}

string s, t;
vector<int>poss[2][26];
int pos[100005];
int main(){
	cin >> s >> t;
	rep(i, s.size()){
		poss[0][s[i]-'a'].pb(i);
	}
	rep(i, t.size()){
		poss[1][t[i]-'a'].pb(i);
	}
	int pre = -1;
	rep(i, s.size()){
		int k = POSU(poss[1][s[i]-'a'], pre);
		if(k == poss[1][s[i]-'a'].size()) goto nxt;
		else pre = poss[1][s[i]-'a'][k];
	}
	cout << -1 << '\n';
	return 0;
	nxt:;
	pre = INF;
	rep(i, 100005) pos[i] = -INF;
	pos[s.size()] = INF;
	for(int i=s.size()-1;i>=0;i--){
		int x = POSL(poss[1][s[i]-'a'], pre);
		x--;
		if(x == -1) break;
		pos[i] = poss[1][s[i]-'a'][x];
		pre = pos[i];
	}
	string ans = "";
	pre = -1;
	int pre2 = -1;
	while(1){
	    bool upd = 0;
		for(char ch='a';ch<='z';ch++){
			int a = POSU(poss[0][ch-'a'], pre);
			if(poss[0][ch-'a'].size() == a) continue;
			if(pos[poss[0][ch-'a'][a]] <= pre2){
				ans.pb(ch);
				pre = poss[0][ch-'a'][a];
				a = POSU(poss[1][ch-'a'], pre2);
				if(a == poss[1][ch-'a'].size()){
					cout << ans << endl;
					return 0;
				}
				pre2 = poss[1][ch-'a'][a];
				upd = 1;
				break;
			}
		}
		if(!upd) assert(false);
	}
}