package com.company;

import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String left = scanner.next();
        String right = scanner.next();
        if(left.length() < right.length())
        {
            System.out.println(right);
            return;
        }
        if(left.length() > right.length())
        {
            System.out.println(left);
            return;
        }
        for(int i = 0;i < left.length();i++)
        {
            char leftValue = left.charAt(i);
            char rightValue = right.charAt(i);
            if(leftValue == rightValue)
            {
                continue;
            }
            if(leftValue == '7' && rightValue == '4')
            {
                System.out.println(right);
                return;
            }
            if(leftValue == '4' && rightValue == '7')
            {
                System.out.println(left);
                return;
            }
            if(leftValue > rightValue)
            {
                System.out.println(left);
                return;
            }
            System.out.println(right);
            return;
        }

    }
}