#define _CRT_SECURE_NO_WARNINGS
#define _SILENCE_CXX17_C_HEADER_DEPRECATION_WARNING

#include <bits/stdc++.h>

using namespace std;
int num[105];
vector<int> ac[105];

int dfs(int x) {
    for (int i = ac[x].size() - 1; i >= 0; i--)
        if (num[ac[x][i]]) {
            num[ac[x][i]]--;
            int res = dfs(ac[x][i]);
            num[ac[x][i]]++;
            if (res == -1) return 1;
        }
    return -1;
}

int main() {
    for (;;) {
        int x;
        scanf("%d", &x);
        num[x]++;
        if (getchar() == '\n') break;
    }
    vector<int> can;
    for (;;) {
        int x;
        if (scanf("%d", &x) == -1)break;
        can.push_back(x);
        if (getchar() == '\n') break;
    }
    sort(can.begin(), can.end());
    for (int i = 1; i <= 100; i++)
        if (num[i]) {
            num[i]--;
            for (int j = 1; j <= 100; j++)
                if (num[j] && (i % j == 0 || j % i == 0))
                    ac[i].push_back(j);
            num[i]++;
        }
    for (int i = 0; i < can.size(); i++) {
        num[can[i]]--;
        if (dfs(can[i]) == -1)return printf("%d", can[i]), 0;
        num[can[i]]++;
    }
    puts("-1");
    return 0;
}