import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.StringTokenizer;

public class Main {

    static BufferedReader in;
    static PrintWriter out;
    static StringTokenizer tok;

    void solve() throws IOException {
        String a = ns();
        String b = ns();

        if (a.length() < b.length()) {
            out.println(b);
            return;
        }
        if (b.length() < a.length()) {
            out.println(a);
            return;
        }

        int[] digitsa = a.chars().map(c -> c - '0').toArray();
        int[] digitsb = b.chars().map(c -> c - '0').toArray();

        for (int i = 0; i < a.length(); i++) {
            if (digitsa[i] != digitsb[i]) {
                if (digitsa[i] == 4 && digitsb[i] == 7) {
                    out.println(a);
                    return;
                } else if (digitsa[i] == 7 && digitsb[i] == 4) {
                    out.println(b);
                    return;
                } else {
                    out.println(digitsa[i] < digitsb[i] ? b : a);
                }
            }
        }
    }

    String ns() throws IOException {
        while (!tok.hasMoreTokens()) {
            tok = new StringTokenizer(in.readLine(), " ");
        }
        return tok.nextToken();
    }

    int ni() throws IOException {
        return Integer.parseInt(ns());
    }

    long nl() throws IOException {
        return Long.parseLong(ns());
    }

    double nd() throws IOException {
        return Double.parseDouble(ns());
    }

    String[] nsa(int n) throws IOException {
        String[] res = new String[n];
        for (int i = 0; i < n; i++) {
            res[i] = ns();
        }
        return res;
    }

    int[] nia(int n) throws IOException {
        int[] res = new int[n];
        for (int i = 0; i < n; i++) {
            res[i] = ni();
        }
        return res;
    }

    long[] nla(int n) throws IOException {
        long[] res = new long[n];
        for (int i = 0; i < n; i++) {
            res[i] = nl();
        }
        return res;
    }

    public static void main(String[] args) throws IOException {
        in = new BufferedReader(new InputStreamReader(System.in));
        out = new PrintWriter(System.out);
        tok = new StringTokenizer("");
        Main main = new Main();
        main.solve();
        out.close();
    }
}