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 Lua (5.3.2) (judge verdict: Accepted)

local n=io.read("*n","*l")
local a={}
for i=1,n do
    local bar=io.read("*n")
    if not a[bar] then
        a[bar]=1
    else
        a[bar]=a[bar]+1
    end
end

local barmax=0
for length,number in pairs(a) do
    if number>1 then
        barmax=math.max(length,barmax)
    end
end
if barmax==0 then
    print(0)
    return
end
if a[barmax]>=4 then
    print(barmax*barmax)
else
    local barmax2=0
    for length,number in pairs(a) do
        if length<barmax and number>1 then
            barmax2=math.max(length,barmax2)
        end
    end
    print(barmax*barmax2)
end