def comp(a, b):
    if a == 4 and b == 7:
        return False
    if a == 7 and b == 4:
        return True
    return a < b


def main():
    a, b = input().split()
    if len(a) != len(b):
        print(a if len(a) > len(b) else b)
    else:
        for i in range(len(a)):
            if a[i] != b[i]:
                if comp(int(a[i]), int(b[i])):
                    print(b)
                    return
                else:
                    print(a)
                    return


if __name__ == '__main__':
    main()