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# (.NET Core 3.1.201) (judge verdict: Wrong Answer)

using System;
using System.Numerics;

namespace ConsoleApp3
{
    class Program
    {
        static void Main(string[] args)
        {
            var split = Console.ReadLine().Split(" ");
            BigInteger a = BigInteger.Parse(split[0]);
            BigInteger b = BigInteger.Parse(split[1]);
            BigInteger c = BigInteger.Parse(split[2]);
            BigInteger d = BigInteger.Parse(split[3]);

            BigInteger answer = -1;
            for(int i = 0; i < 11; ++ i)
            {
                answer *= 10;
            }

            if (BigInteger.Multiply(a, c) > answer) answer = BigInteger.Multiply(a, c);
            if (BigInteger.Multiply(b, c) > answer) answer = BigInteger.Multiply(b, c);
            if (BigInteger.Multiply(a, d) > answer) answer = BigInteger.Multiply(a, d);
            if (BigInteger.Multiply(b, d) > answer) answer = BigInteger.Multiply(b, d);

            Console.WriteLine(answer);
        }
    }
}