import java.util.Scanner;

public class Test {
	public static Scanner sc = new Scanner(System.in);

	public static void main(String[] args) {
		String s1 = sc.next(), s2 = sc.next();
		char c1, c2;
		if (s1.length() < s2.length()) {
			System.out.println(s2);
			return;
		} else if (s1.length() > s2.length()) {
			System.out.println(s1);
			return;
		} else {
			for (int i = 0; i < s1.length(); i++) {
				c1 = s1.charAt(i);
				c2 = s2.charAt(i);
				if (c1 == '4' && c2 == '7') {
					System.out.println(s1);
					return;
				} else if (c1 == '7' && c2 == '4') {
					System.out.println(s2);
					return;
				} else if (c1 > c2) {
					System.out.println(s1);
					return;
				} else if (c1 < c2) {
					System.out.println(s2);
					return;
				}
			}
		}
	}
}