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 C (GCC 9.2.1) (judge verdict: Accepted)

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<math.h>
#define PI 3.141592653589793
#define MOD 1000000007
//#define DEBUG



//qsort用、昇順
int compare_int(const void *a, const void *b)
{
	return *(int*)a-*(int*)b;
}
//qsort(array, 10, sizeof(int), compare_int)



int main(){
	long long int a, b, c, d;
	scanf("%lld%lld%lld%lld", &a, &b, &c, &d);
	long long int x, y, z, w;
	x = a*c;
	y = a*d;
	z = b*c;
	w = b*d;
	if(x<y) x = y;
	if(x<z) x = z;
	if(x<w) x = w;

	printf("%lld\n", x);
	
	return 0;
}