Problem Statement

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 $x \times y$?

Input

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

Output

Print the answer.

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.

Sample Input 1

1 2 1 1

Sample Output 1

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.

Sample Input 2

3 5 -4 -2

Sample Output 2

-6

The answer can be negative.

Sample Input 3

-1000000000 0 -1000000000 0

Sample Output 3

1000000000000000000

见题面 Input 部分

见题面 Output 部分