package yukicoder;
import java.util.Scanner;
public class Main{
	public static void main(String[] args)throws Exception{
		new Main().solve();
	}
	void solve(){
		Scanner sc=new Scanner(System.in);
		String s1=sc.next();
		String s2=sc.next();
		char[] c1=s1.toCharArray();
		char[] c2=s2.toCharArray();
		if(c1.length>c2.length){
			System.out.println(s1);
		}else if(c1.length<c2.length){
			System.out.println(s2);
		}else if(c1.length==c2.length){
			for(int i=0;i<c1.length;i++){
				if(c1[i]=='4'&&c2[i]=='7'){
					System.out.println(s1);
				}else if(c1[i]=='7'&&c2[i]=='4'){
					System.out.println(s2);
				}else if(c1[i]>c2[i]){
					System.out.println(s1);
				}else if(c1[i]<c2[i]){
					System.out.println(s2);
				}else{
					continue;
				}
				return;
			}
		}
		
	}
}