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# (Mono-mcs 6.8.0.105) (judge verdict: Accepted)

using System;
using System.Linq;
using System.Text;
using System.Collections;
using System.Collections.Generic;

namespace AtCoder
{
	class Program
	{
		static void Main(string[] args)
		{
			var n = ReadLineLongSplit();
			var a = n[0];
			var b = n[1];
			var c = n[2];
			var d = n[3];

			var ans = new List<long>();
			ans.Add(a*c);
			ans.Add(a*d);
			ans.Add(b*c);
			ans.Add(b*d);

			Console.WriteLine(ans.Max());
		}

		public static int nCm(int n, int m)
		{
			if (n == 0) return 0;
			if (m == 0) return 1;
			return n * nCm(n - 1, m - 1) / m;
		}

		public static string ReadLine()
		{
			return Console.ReadLine();
		}

		public static int ReadLineInt()
		{
			return int.Parse(ReadLine());
		}

		public static long ReadLineLong()
		{
			return long.Parse(ReadLine());
		}

		public static string[] ReadLineStringSplit(char s = ' ')
		{
			return ReadLine().Split(s).ToArray();
		}

		public static int[] ReadLineIntSplit(char s = ' ')
		{
			return ReadLine().Split(s).Select(x => int.Parse(x)).ToArray();
		}

		public static long[] ReadLineLongSplit(char s = ' ')
		{
			return ReadLine().Split(s).Select(x => long.Parse(x)).ToArray();
		}
	}
}