#define _CRT_SECURE_NO_WARNINGS
#include <bits/stdc++.h>
using namespace std;
using std::chrono::high_resolution_clock;
typedef long long ll;
typedef long double ld;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef pair<int, int>pi;
typedef pair<ll, ll>pl;
typedef vector<pi>vpi;
typedef vector<pl>vpl;
typedef vector<vi> vvi;
typedef vector<vl> vvl;
typedef vector<string> vs;
const double PI = acos(-1);
const int oo = 1e9 + 7;
const int mod = 1e9 + 7;
const int N = 1e6 + 1;
#define endl '\n'
#define all(v) (v).begin(),(v).end() 
#define rall(v) (v).rbegin(),(v).rend()
#define f first
#define st second
#define pb push_back
#define read(v) for (auto& it : v) scanf("%d", &it);
#define readL(v) for (auto& it : v) scanf("%lld", &it);
#define print(v) for (auto it : v) printf("%d ", it); puts("");
#define printL(v) for (auto it : v) printf("%lld ", it); puts("");
auto Time() {
	return high_resolution_clock::now();
}
void solve() {
	string a, b;
	cin >> a >> b;
	int n = a.size(), m = b.size();
	for (int i = 0; i < n; i++) {
		string curA = a.substr(0, (i + 1));
		for (int j = m - 1; j >= 0; j--) {
			string curB = b.substr(j);
			string copA = curB + a.substr(i + 1);
			string copB = b.substr(0, j) + curA;
			if (copA == copB) {
				puts(copA.c_str());
				return;
			}
		}
	}
	puts("-1");
}
int t = 1;
int main() {
#ifndef ONLINE_JUDGE
	freopen("input.txt", "r", stdin);
#endif
	//scanf("%d", &t);
	while (t--) solve();
}