Problem:
Score : 300 points

Problem Statement

We have N sticks with negligible thickness.
The length of the i-th stick is A_i.

Snuke wants to select four different sticks from these sticks and form a rectangle (including a square), using the sticks as its sides.
Find the maximum possible area of the rectangle.

Constraints

4 \leq N \leq 10^5

1 \leq A_i \leq 10^9

A_i is an integer.

Input

Input is given from Standard Input in the following format:

N
A_1 A_2 ... A_N

Output

Print the maximum possible area of the rectangle.
If no rectangle can be formed, print 0.

Sample Input 1

6
3 1 2 4 2 1

Sample Output 1

2

1 \times 2 rectangle can be formed.

Sample Input 2

4
1 2 3 4

Sample Output 2

0

No rectangle can be formed.

Sample Input 3

10
3 3 3 3 4 4 4 5 5 5

Sample Output 3

20

Solution in Fortran (gfortran v4.8.4) (judge verdict: Accepted)

program main
    integer n
    integer :: a(10**5)
    integer, allocatable :: str_a(:)
    integer, allocatable :: ans(:)
    integer(8) :: first=0, second=0
    integer(8) :: answer
    integer restart
 
    read *, n
    read *, (a(i), i=1,n)
    str_a = a(1:n)
    ans = quick(str_a)
    
    do i=1,n-1
        if(ans(i)==ans(i+1)) then
            first = ans(i)
            restart = i+2
            exit
        end if
    end do
 
    if (result < n) then
        do i=restart,n-1
            if(ans(i)==ans(i+1)) then
                second = ans(i)
                exit
            end if
        end do
    end if
    
    answer = first * second
    print *, answer
 
contains
    recursive function quick(a) result(r)
        integer, intent(in) :: a(:)
        integer, allocatable :: r(:)
        integer :: p
        if(size(a) < 2) then
            r = a
        else
            p = a(1)
            r = [quick(pack(a(2:), a(2:) > p)), pack(a, a == p), quick(pack(a(2:), a(2:) < p))]
        end if
    end function quick
end program main