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)

parseInt(x::String) = parse(Int, x)
parseInt(x::SubString{String}) = parse(Int, x)
parseInt(x::Char) = parse(Int, x)
parseInt(x::Float64) = trunc(Int, x)
parseFloat(x::String) = parse(Float64, x)
parseFloat(x::Int) = trunc(Float64, x)
parseFloat(x::SubString{String}) = parse(Float64, x)
parseFloat(x::Char) = parse(Float64, x)
parseMap(x::Array{SubString{String},1}) = map(parseInt, x)

function main()
    n=parseInt(readline())
    a=sort(parseMap(split(readline())),rev=true)
    cnt=Dict{Int,Int}()
    for i in a
        if haskey(cnt,i)
            cnt[i]+=1
        else
            cnt[i]=1
        end
    end
    hoge=sort(collect(cnt),by=x->x[1],rev=true)
    cnt=0
    ans=0
    for (i,j) in hoge
        if j>=4
            ans=i^2
        elseif j>=2
            if cnt==0
                ans=i
                cnt+=1
            else
                ans*=i
                break
            end
        end
    end
    println(ans)
end
main()