#include <map>
#include <set>
#include <cmath>
#include <queue>
#include <stack>
#include <bitset>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
#include <functional>
#include <unordered_set>
#include <unordered_set>

using u32 = unsigned;
using i64 = long long;
using u64 = unsigned long long;
using i128 = __int128;

std::vector<int> Z(std::string s) {
    int n = s.size();
    std::vector<int> z(n + 1);
    z[0] = n;
    for (int i = 1, j = 1; i < n; i++) {
        z[i] = std::max(0, std::min(j + z[j] - i, z[i - j]));
        while (i + z[i] < n && s[z[i]] == s[i + z[i]]) {
            z[i]++;
        }
        if (i + z[i] > j + z[j]) {
            j = i;
        }
    }
    return z;
}

void solve() {
	std::string a, b;
	std::cin >> a >> b;

	// auto z = Z(a);
	// for (int i: z) {
	// 	std::cout << i << " ";
	// }

	int n = a.size();
	int idx = -1;
	for (int i = 0; i < n; i++) {
		if (b[i] == '1') {
			idx = i;
			break;
		}
	}

	if (idx == -1) {
		std::cout << "tpchkrltdsjklsdvnskdvjsdfosdf\n";
		return;
	}

	auto c = a.substr(idx);
	auto z = Z(c);
	int m = c.size();
	int len = m;
	for (int i = 0; i < m; i++) {
		if (b[i + idx] == '1') {
			len = std::min(len, z[i]);
		}
	}
	auto res = c.substr(0, len);
	res += a;
	z = Z(res);
	for (int i = len; i < len + n; i++) {
		if (b[i - len] == '0' && z[i] >= len) {
			std::cout << "-1\n";
			return;
		}
	}
	std::cout << res.substr(0, len) << "\n";
}

int main() {
	std::ios::sync_with_stdio(false);
	std::cin.tie(nullptr), std::cout.tie(nullptr);

	int T = 1;
	// std::cin >> T;
	while (T--) {
		solve();
	}

	return 0;
}