import java.io.*;

// 処理
class Process {
    private String[] S;
    private String[] P;
    private String[] X;

    Process(String[] S, String[] P, String[] X) {
        this.S = S;
        this.P = P;
        this.X = X;
    }

    String getResult() {
        if(P[0].equals(P[1])) {
            return "-1";
        }

        if(P[0].length() > P[1].length()) {
            return S[0];
        }

        if(P[0].length() < P[1].length()) {
            return S[1];
        }

        for(int i = 0; i < P[0].length(); i++) {
            if(P[0].charAt(i) > P[1].charAt(i)) {
                return S[0];
            }
            
            if(P[0].charAt(i) < P[1].charAt(i)) {
                return S[1];
            }
        }

        return "";
    }
}

public class Main {
    public static void main(String[] args) throws IOException {
        var bufferedReader = new BufferedReader(new InputStreamReader(System.in));
        var printWriter    = new PrintWriter(new BufferedWriter(new OutputStreamWriter(System.out)));

        // 入力
        var S = new String[2];
        var P = new String[2];
        var X = new String[2];
        for(int i = 0; i < 2; i++) {
            String[] input = bufferedReader.readLine().trim().split("[ ]+");
            S[i] = input[0];
            P[i] = input[1];
            X[i] = input[2];
        }

        // 出力
        printWriter.println((new Process(S, P, X)).getResult());

        bufferedReader.close();
        printWriter.close();
    }
}