from sys import stdin





def main():

    _in = [_.rstrip() for _ in stdin.readlines()]

    a, b, c, d = list(map(int, _in[0].split(' ')))  # type:list(int)

    # vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv

    cnt = -float('inf')

    cnt = max(cnt, a * c)

    cnt = max(cnt, a * d)

    cnt = max(cnt, b * c)

    cnt = max(cnt, b * d)

    ans = cnt

    # ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

    print(ans)





if __name__ == "__main__":

    main()

from sys import stdin





def main():

    _in = [_.rstrip() for _ in stdin.readlines()]

    a, b, c, d = list(map(int, _in[0].split(' ')))  # type:list(int)

    # vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv

    ans = -float('inf')

    for _ in [a * c, a * d, b * c, b * d]:

        ans = max(ans, _)

    # ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

    print(ans)





if __name__ == "__main__":

    main()

from sys import stdin


def main():
    _in = [_.rstrip() for _ in stdin.readlines()]
    a, b, c, d = list(map(int, _in[0].split(" ")))  # type:list(int)
    # vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
    cnt = -float("inf")
    cnt = max(cnt, a * c)
    cnt = max(cnt, a * d)
    cnt = max(cnt, b * c)
    cnt = max(cnt, b * d)
    ans = cnt
    # ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    print(ans)


if __name__ == "__main__":
    main()

from sys import stdin


def main():
    _in = [_.rstrip() for _ in stdin.readlines()]
    a, b, c, d = list(map(int, _in[0].split(" ")))  # type:list(int)
    # vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
    ans = -float("inf")
    for _ in [a * c, a * d, b * c, b * d]:
        ans = max(ans, _)
    # ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    print(ans)


if __name__ == "__main__":
    main()

-    cnt = -float("inf") -    cnt = max(cnt, a * c) -    cnt = max(cnt, a * d) -    cnt = max(cnt, b * c) -    cnt = max(cnt, b * d) -    ans = cnt +    ans = -float("inf") +    for _ in [a * c, a * d, b * c, b * d]: +        ans = max(ans, _)