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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 $x \times y$?

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