#include <bits/stdc++.h>

#define rep(i, n) for (int (i) = 0; (i) < (int)(n); (i)++)

const int dx[] = {1, 0, -1, 0};
const int dy[] = {0, 1, 0, -1};
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vll;

bool cmp(const string& s, const string& t) {
    int n = s.size();
    int m = t.size();
    if (n < m) return true;
    if (n > m) return false;
    for (int i = 0; i < n; i++) {
        if (s[i] > t[i]) return false;
        if (s[i] < t[i]) return true;
    }
    return true;
}

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    string s, t, pa, pb, xa, xb;
    cin >> s >> pa >> xa;
    cin >> t >> pb >> xb;
    if (pa == pb) cout << -1 << endl;
    else {
        if (cmp(pa, pb)) cout << t << endl;
        else cout << s << endl;
    }
    return 0;
}