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();
    String ans = "";
    if(a.length() > b.length()) {
      ans = a;
    } else if(a.length() < b.length()) {
      ans = b;
    } else {
      for(int i = 0; i < a.length(); i++) {
        int num1 = Integer.parseInt(String.valueOf(a.charAt(i)));
        int num2 = Integer.parseInt(String.valueOf(b.charAt(i)));
        if(num1 > num2) {
          if(num1 == 7 && num2 == 4) {
            ans = b;
          } else {
            ans = a;
          }
        } else if(num1 < num2) {
          if(num1 == 4 && num2 == 7) {
            ans = a;
          } else {
            ans = b;
          }
        }
      }
    }
    System.out.println(ans);
  }
}