# -*- coding: utf-8 -*-
"""
No.293 4>7の世界
https://yukicoder.me/problems/no/293

"""
import sys
from sys import stdin
input = stdin.readline


class Number:
    def __init__(self, s):
        self.s = s

    def __lt__(self, other):
        if len(self.s) < len(other.s):
            return True
        elif len(self.s) == len(other.s):
            for a, b in zip(self.s, other.s):
                if a != b:
                    if (a == '4' and b == '7') or (a == '7' and b == '4'):
                        return not a < b
                    else:
                        return a < b
            return False
        else:
            return False

    def __str__(self):
        return self.s


def main(args):
    A, B = map(Number, input().split())
    if A < B:
        print(B)
    else:
        print(A)


if __name__ == '__main__':
    main(sys.argv[1:])