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 Fortran (GNU Fortran 9.2.1) (judge verdict: Wrong Answer)

program Main
implicit none
    integer(16) ans,a,b,c,d,x,y
    read (*,*) a, b, c, d
    x=max(a,b)
    y=max(c,d)
    if ((x>0.and.y>0)) then
        ans=x*y
    else if(x<1 .and.y<1) then
        x=min(a,b)
        y=min(b,c)
        ans=x*y
    else if(x<0) then
        y=min(c,d)
        ans=x*y
    else 
        x=min(a,b)
        ans=x*y
    end if
    write(*,*) ans
end program Main