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 Ruby (2.7.1) (judge verdict: Accepted)

line = gets.split(' ').map(&:to_i)

if line == [0, 0, 0, 0]
  puts 0
  exit
end

f = line[0,2]
s = line[2,2]

line.reject!{|x| x == 0}
f.reject!{|x| x == 0}
s.reject!{|x| x == 0}
arr = []
f.each do |x|
  s.each do |y|
    arr << x * y
  end
end

puts arr.max