import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.InputMismatchException;
import java.io.OutputStream;
import java.util.StringTokenizer;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.HashMap;
import java.util.Map;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
import java.math.BigDecimal;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        Task solver = new Task();
        solver.solve(1, in, out);
        out.close();
    }

    static class Task {
        public void solve(int testNumber, InputReader in, PrintWriter out) {
            String[] S = new String[2];
            String[] P = new String[2];
            String[] X = new String[2];
            for(int i=0; i<2; i++){
                S[i] = in.next();
                P[i] = in.next();
                X[i] = in.next();
            }
            int win=-1;
            if(P[0].length()<P[1].length()){
                out.println(S[1]);
                return;
            }
            if(P[0].length()>P[1].length()){
                out.println(S[0]);
                return;
            }
            for(int i=0; i<P[0].length(); i++){
                if(P[0].charAt(i)>P[1].charAt(i)){
                    win=0;
                    break;
                }
                if(P[0].charAt(i)<P[1].charAt(i)){
                    win=1;
                    break;
                }
            }
            if(win==-1) out.println(-1);
            else out.println(S[win]);
        }
    }


    static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }

        public long nextLong() {
            return Long.parseLong(next());
        }

    }
}