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 Julia (0.5.0) (judge verdict: Wrong Answer)

N = parse(Int,readline())
A = map(x->parse(Int,x), split(readline()))
#A = parse.(Int, split(readline()))

count = Dict()

for a in A
    count[a] = get(count,a,0) + 1
end

count2 = sort([x for x in count if x.second >= 2],by = x->x.first,rev = true)
count4 = sort([x for x in count if x.second >= 4],by = x->x.first,rev = true)

ans = 0

if length(count2) > 2
    ans = count2[1].first * count2[2].first
end

if length(count4) > 0
    ans = max(ans, count4[1].first * count4[1].first)
end

if length(count2) > 1 && length(count4) > 1
    ans = max(ans, count2[1].first * count4[1].first)
end

println(ans)