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 OCaml (4.10.0) (judge verdict: Accepted)

let () =
  Scanf.scanf "%d %d %d %d\n" @@ fun a b c d ->
  Printf.printf "%d\n"
    (if a < 0 && c < 0 then
       if b > 0 && d > 0 then max (a*c) (b*d)
       else a*c
     else if a > 0 && c > 0 || b > 0 && d > 0 then b*d
     else if a <= 0 && 0 <= b || c <= 0 && 0 <= d then 0
     else max (a*d) (b*c))