import java.util.Scanner;

/**
 * Created by scache on 15/10/23.
 */
public class Main293 {
    public static void main(String[] args){
        new Main293();
    }

    public Main293(){
        Scanner sc = new Scanner(System.in);
        String A = sc.next();
        String B = sc.next();

        String ret = A;
        if(A.length()!=B.length()) {
            ret = A.length() > B.length() ? A : B;
        }else{
            for(int i=0;i<A.length();i++) {
                if (A.charAt(i) == '4' && B.charAt(i) == '7' || A.charAt(i) == '7' && B.charAt(i) == '4') {
                    ret = A.charAt(i) == '4' ? A : B;
                    break;
                }

                if (A.charAt(i) != B.charAt(i)) {
                    ret = A.charAt(i) > B.charAt(i) ? A : B;
                    break;
                }
            }
        }

        System.out.println(ret);

    }

    private void solve(){

    }

}