import java.util.Scanner;

public class Main{
	public static void main(String[] args){
        Scanner sc=new Scanner(System.in);
        while(sc.hasNext()){
        	String a=sc.next();
        	String b=sc.next();
        	if(a.length()>b.length()) System.out.println(a);
        	else if(a.length()<b.length()) System.out.println(b);
        	else{
        		for(int i=0;i<a.length();i++){
        			if(a.charAt(i)==b.charAt(i)) continue;
        			else{
        				int ka=a.charAt(i)-'0';
        				int kb=b.charAt(i)-'0';
        				if(ka>kb){
        					if(ka==7 && kb==4) System.out.println(b);
        					else System.out.println(a);
        				}
        				else{
        					if(kb==7 && ka==4) System.out.println(a);
        					else System.out.println(b);
        				}
        				break;
        			}
        		}
        	}
        }
    }
}