import java.util.Scanner;

public class Main {

	@SuppressWarnings("resource")
	public static void main(String args[]) {
		Scanner scanner = new Scanner(System.in);
		int a=scanner.nextInt();
		int b=scanner.nextInt();
		String sa=String.valueOf(a);
		String sb=String.valueOf(b);
		if(sa.length()>sb.length()){
			System.out.println(sa);
		}else if(sa.length()<sb.length()){
			System.out.println(sb);
		}else{
			for(int i=0;i<sa.length();i++){
				int ta=sa.charAt(i)-'0';
				int tb=sb.charAt(i)-'0';
				if((ta>tb&&!(ta==7&&tb==4))||(ta==4&&tb==7)){
					System.out.println(sa);
					return;
				}else if((tb>ta&&!(ta==4&&tb==7))||(ta==7&&tb==4)){
					System.out.println(sb);
					return;
				}
			}
		}
		
	}
}