import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		String A = scan.next();
		String B = scan.next();
		scan.close();
		int l1 = A.length();
		int l2 = B.length();
		if(l1 > l2) {
			System.out.println(A);
		}else if(l1 < l2) {
			System.out.println(B);
		}else {
			for(int i = 0; i < l1; i++) {
				char c1 = A.charAt(i);
				char c2 = B.charAt(i);
				if(c1 == '4' && c2 == '7') {
					System.out.println(A);
					System.exit(0);
				}else if(c1 == '7' && c2 == '4') {
					System.out.println(B);
					System.exit(0);
				}else if(c1 > c2) {
					System.out.println(A);
					System.exit(0);
				}else if(c1 < c2) {
					System.out.println(B);
					System.exit(0);
				}
			}
		}

	}
}