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: Wrong Answer)

#include <stdio.h>
int main(int argc, char *argv[]) {

int a, b,c, d, x, y, k;
  scanf("%d", &a);
  scanf("%d", &b);
  scanf("%d", &c);
  scanf("%d", &d);
  
	a<=x&&x<=b;
  	c<=y&&y<=d;

	if(a>0&&c>0){
    k=b*d;
    }
	if(a<0&&c>0){
    k=b*c;
    }
  	if(a>0&&c<0){
    k=a*d;
    }
  else {
  k = b*d;
  }
  printf("%d",k);
}