import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        try (Scanner scan = new Scanner(System.in)) {
            String a = scan.next();
            String b = scan.next();
            
            if(a.length() == b.length() ) {
                for(int i=0; i<a.length(); i++) {
                    char chA = a.charAt(i);
                    char chB = b.charAt(i);
                    if(chA == chB) {
                        continue;
                    } else {
                        if(chA == '4' && chB == '7') {
                            System.out.println(a);
                        } else if(chA == '7' && chB == '4') {
                            System.out.println(b);
                        } else {
                            System.out.println(chA > chB? a:b);
                        }
                        break;
                    }
                }
                
            } else if(a.length() > b.length()) {
                System.out.println(a);
            } else {
                System.out.println(b);
            }
        }
    }
}