#include <cstdio>

#include <iostream>

#include <cstring>

#include <algorithm>

using namespace std;

int t1,h,ff,num;

int a[10010],b[10010],vis[10010];

int pd(int s)

{

	int kk=0;

	for (int i=0;i<t1;i++)

		if(!vis[i] && (s % a[i]==0 || a[i] % s==0))

		{

			kk++;

			num=(num+1) % 2;

			vis[i]=1;

			if (pd(a[i])){	

				vis[i]=0;

				num=(num+1)%2;

				return 0;

			}

			vis[i]=0;

			num=(num+1) % 2;

		}

	if (!kk || !num) return 1;

}

int cmp(int a,int b)

{

	return a<b;

}

int main()

{

	char s[10010];

	memset(a,0,sizeof(a));

	memset(b,0,sizeof(b));

	gets(s);

	int l=strlen(s),i=0;

	t1=0;

	while(i<l)

	{

		int k=0;

		while (s[i]!=' ' && i<l)

		{

			k=k*10+s[i]-'0';

			i++;

		}

		a[t1++]=k;

		i++;

	}

	gets(s);

	l=strlen(s);

	int t=0;

	i=0;

	while (i<l)

	{

		int k=0;

		while (s[i]!=' ' && i<l)

		{

			k=k*10+s[i]-'0';

			i++;

		}

		b[t++]=k;

		i++;

	}

	sort(b,b+t,cmp);

	int f=0;

	for (i=0;i<t;i++)

	{

		memset(vis,0,sizeof(vis));

		for (int j=0;j<t1;j++)

			if (b[i]==a[j])

			{

				vis[j]=1;

				break;

			}

		num=0;

		ff=0;

		if (pd(b[i]))

		{

			printf("%d\n",b[i]);

			f=1;

			break;

		}

	}

	if (!f) printf("-1\n");

	return 0;

}