Given are integers a,b,c and d.
If x and y are integers and $a \leq x \leq b$ and $c\leq y \leq d$ hold, what is the maximum possible value of $x \times y$?

-----Constraints-----
- -$10^9 \leq a \leq b \leq 10^9$
- -$10^9 \leq c \leq d \leq 10^9$
- All values in input are integers.

-----Input-----
Input is given from Standard Input in the following format:
a b c d

-----Output-----
Print the answer.

-----Sample Input-----
1 2 1 1

-----Sample Output-----
2

If x = 1 and y = 1 then $x \times y = 1$.
If x = 2 and y = 1 then $x \times y = 2$.
Therefore, the answer is 2.

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