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 Java (OpenJDK 11.0.6) (judge verdict: Accepted)

import java.util.Scanner;

/**
 * B - Product Max
 * 整数 a,b,c,d が与えられます。
 * a≤x≤b,c≤y≤d を満たす整数 x,y について、x×y の最大値はいくつですか。
 */
public class Main {

    public static void main( String[] args ) {

        Scanner sc = new Scanner( System.in );
        // 入力値
        long a = sc.nextLong();
        long b = sc.nextLong();
        long c = sc.nextLong();
        long d = sc.nextLong();

        long[] vals = {a * c, a * d, b * c, b * d};
        long max = vals[0];
        for ( int i = 1; i < vals.length; i++ ) {
            max = Math.max( max, vals[i] );
        }

        System.out.println( max );

        sc.close();
    }
}