import core.bitop;
import std.algorithm;
import std.ascii;
import std.bigint;
import std.conv;
import std.functional;
import std.math;
import std.numeric;
import std.range;
import std.stdio;
import std.string;
import std.random;
import std.typecons;
import std.container;

alias sread = () => readln.chomp();
ulong MOD = 1_000_000_007;
ulong INF = 1_000_000_000_000;
ulong MIDDLE = 100_000;
alias Pair = Tuple!(long, "flag", long, "num");

T lread(T = long)()
{
    return readln.chomp.to!T();
}

T[] aryread(T = long)()
{
    return readln.split.to!(T[])();
}

void scan(TList...)(ref TList Args)
{
    auto line = readln.split();
    foreach (i, T; TList)
    {
        T val = line[i].to!(T);
        Args[i] = val;
    }
}

void main()
{
    auto n = lread();
    auto a = aryread();
    auto wood = new Pair[](0);
    a.sort();
    long iter;

    while(iter < n)
    {
        long tmp = a[iter], cnt = 1;
        while(iter + 1 < n && tmp == a[iter + 1])
            iter++, cnt++;
        wood ~= Pair(tmp, cnt / 2);
        iter++;
    }
    wood.sort!"a.flag > b.flag"();
    long row, hei;
    foreach(e; wood)
    {
        if(e.num > 1 && !row && !hei)
        {
            row = hei = e.flag;
            break;
        }
        
        if(e.num && !row)
            row = e.flag;
        else if(e.num && !hei)
            hei = e.flag;
    }
    writeln(row * hei);
}
