import java.util.*;
public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		String a = sc.next();
		String b = sc.next();
		
		if(a.length()<b.length()){
			System.out.println(b);
		}else if(a.length()>b.length()){
			System.out.println(a);
		}else{
			for(int i=0;i<a.length();i++){
				if(a.charAt(i)==b.charAt(i)) continue;
				if(a.charAt(i)=='4'&&b.charAt(i)=='7'){
					System.out.println(a);
				}else if(a.charAt(i)=='7'&&b.charAt(i)=='4'){
					System.out.println(b);
					
				}else{
					if((int)a.charAt(i)<(int)b.charAt(i)){
						System.out.println(b);
					}else{
						System.out.println(a);
					}
				}
				return;
			}
		}
	}
}