#include<bits/stdc++.h>
#define pt putchar
using namespace std;
typedef long long ll;
const int N=1e6+5;
const int mod1=998244353,mod2=1e9+9,B=517;
int read();
void write(int x);
int n,p;
char s[N],t[N];

ll pw1[N],pw2[N],h1[N],h2[N];

bool check(int l){
	for(int i=1;i+l-1<=n;i++){
		int eq=(((h1[i+l-1]-h1[i-1])*pw1[p]-(h1[p+l-1]-h1[p-1])*pw1[i])%mod1)+(((h2[i+l-1]-h2[i-1])*pw2[p]-(h2[p+l-1]-h2[p-1])*pw2[i])%mod2)==0;
		if(eq==1&&t[i]=='0'){
			return 0;//duan l
		}
		if(eq==0&&t[i]=='1'){
			return 1;//chang l
		}
	}
	for(int i=p;i<=p+l-1;i++){
		pt(s[i]);
	}
	exit(0);
	return 1;
}

int main(){
	scanf("%s",s+1);
	scanf("%s",t+1);
	p=n=strlen(s+1);
	pw1[0]=pw2[0]=1;
	for(int i=1;i<=n;i++){
		pw1[i]=pw1[i-1]*B%mod1;
		pw2[i]=pw2[i-1]*B%mod2;
		h1[i]=(h1[i-1]+s[i]*pw1[i])%mod1;
		h2[i]=(h2[i-1]+s[i]*pw2[i])%mod2;
	}
	while(p>=1){
		if(t[p]=='1'){
			break;
		}
		else if(p==1){
			puts("iakioi");return 0;
		}
		p--;
	}
	int l=1,r=n-p+1;
	while(l<=r){
		int mid=(l+r)/2;
		if(check(mid)){
			r=mid-1;
		}
		else{
			l=mid+1;
		}
	}
	puts("-1");
	return 0;
}

int read(){
	int x=0,f=1;
	char c=getchar();
	while(c<'0'||c>'9'){
		if(c=='-'){
			f=-1;
		}
		c=getchar();
	}
	while('0'<=c&&c<='9'){
		x=x*10+c-'0';
		c=getchar();
	}
	return x*f;
}
void write(int x){
	if(x<0){
		pt('-');
		x=-x;
	}
	if(x>9){
		write(x/10);
	}
	pt(x%10+'0');
}