import java.util.*;
import java.io.*;

public class Main {
    public static void main(String[] args) throws Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String[] first = br.readLine().split(" ", 3);
        String[] second = br.readLine().split(" ", 3);
        int winner = -1;
        char[] fArr = first[1].toCharArray();
        char[] sArr = second[1].toCharArray();
        if (fArr.length < sArr.length) {
            winner = 1;
        } else if (fArr.length > sArr.length) {
            winner = 0;
        } else {
            for (int i = 0; i < fArr.length; i++) {
                if (fArr[i] < sArr[i]) {
                    winner = 1;
                    break;
                } else if (fArr[i] > sArr[i]) {
                    winner = 0;
                    break;
                }
            }
        }
        if (winner == -1) {
            System.out.println(-1);
        } else if (winner == 0) {
            System.out.println(first[0]);
        } else {
            System.out.println(second[0]);
        }
    }
}