import java.util.Scanner;

class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String A = sc.next(), B = sc.next();
		sc.close();
		if (A.length() > B.length()) System.out.print(A);
		else if (A.length() < B.length()) System.out.print(B);
		else {
			for (int i = 0; i < A.length(); ++i) {
				if (A.charAt(i) == '4' && B.charAt(i) == '7') {
					System.out.print(A);
					break;
				}
				else if (A.charAt(i) == '7' && B.charAt(i) == '4') {
					System.out.print(B);
					break;
				}
				else if (A.charAt(i) > B.charAt(i)) {
					System.out.print(A);
					break;
				}
				else if (A.charAt(i) < B.charAt(i)) {
					System.out.print(B);
					break;
				}
			}
		}
	}
}