Problem:
Score : 200 points

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.

Input

Input is given from Standard Input in the following format:

a b c d

Output

Print the answer.

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

Solution in PHP (7.4.4) (judge verdict: Wrong Answer)

<?php
$n = explode(" ", trim(fgets(STDIN)));
$a = $n[0];
$b = $n[1];
$c = $n[2];
$d = $n[3];
if ($a >= 0 && $b >= 0) {
    if ($c >= 0 && $d >= 0) {
        echo $b * $d;
    } elseif ($c < 0 && $d >= 0) {
        echo $b * $d;
    } else {
        echo $a * $d;
    }
} elseif ($a < 0 && $b >= 0) {
    if ($c >= 0 && $d >= 0) {
        echo $b * $d;
    } elseif ($c < 0 && $d >= 0) {
        if (abs($a + $c) > abs($b + $d)) {
            echo $a * $c;
        } else {
            echo $b * $d;
        }
    } else {
        echo $a * $c;
    }
} else {
    if ($c >= 0 && $d >= 0) {
        echo $b * $d;
    } elseif ($c < 0 && $d >= 0) {
        echo $a * $c;
    } else {
        echo $a * $c;
    }
}