#include<bits/stdc++.h>
using namespace std;
typedef long long ll;

#define N 1000000

int i,j,k,n,m,t,p,f[N+50];
string s,s2,s3;

int main(){
	ios::sync_with_stdio(0); cin.tie(0);
	cin>>s>>s2; n=s.size(); s="$"+s; s2="$"+s2;
	for(auto &c:s2)c-='0';
	for(i=1;i<=n;i++)if(s2[i])p=i;
	if(!p){cout<<s.substr(1)+"x"; return 0;}
	int l=1,r=n-p+1,md;
	while(l<=r){
		md=(l+r)/2;
		s3="$"+s.substr(p,md);
		for(i=2,j=0;i<=md;i++){
			while(j&&s3[j+1]!=s3[i])j=f[j];
			if(s3[j+1]==s3[i])j++; f[i]=j;
		}
		for(i=1,j=0;i<=n;i++){
			while(j&&s3[j+1]!=s[i])j=f[j];
			if(s3[j+1]==s[i])j++;
			if(i<md)continue;
			
			if(j==md){
				if(!s2[i-md+1]){
					l=md+1; goto aaa;
				}
				j=f[j];
			}
			else{
				if(s2[i-md+1]){
					r=md-1; goto aaa;
				}
			}
		}
		cout<<s3.substr(1); return 0;
		aaa:;
	}
	cout<<-1;
}