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: Accepted)

<?php

class Scanner
{
    private $arr = [];
    private $count = 0;
    private $pointer = 0;

    public function next()
    {
        if ($this->pointer >= $this->count) {
            $str = trim(fgets(STDIN));
            $this->arr = explode(' ', $str);
            $this->count = count($this->arr);
            $this->pointer = 0;
        }
        $result = $this->arr[$this->pointer];
        ++$this->pointer;

        return $result;
    }

    public function hasNext()
    {
        return $this->pointer < $this->count;
    }

    public function nextInt()
    {
        return (int) $this->next();
    }

    public function nextDouble()
    {
        return (float) $this->next();
    }
}

$sc = new Scanner();
$a = $sc->nextInt();
$b = $sc->nextInt();
$c = $sc->nextInt();
$d = $sc->nextInt();

$answer = max($a*$c, $a*$d, $b*$c, $b*$d);

echo $answer.PHP_EOL;