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(void) {

	long long int a, b, c, d, i, j, x, y, mul=0, ans=0;

	scanf("%lld %lld %lld %lld", &a, &b, &c, &d);

	ans = a * c;
	x = a;
	y = c;

	if (x < 0 && y < 0) {
		printf("%lld", ans);
	}
	else {
		for (i = 0; i <= b - a; i++) {
			for (j = 0; j <= d - c; j++) {
				mul = x * y;
				if (mul > ans) {
					ans = mul;
				}
				mul = 0;
				y++;
			}
			x++;
			y = c;
		}

		printf("%lld", ans);
	}

	return 0;
}