#define STOPIT
#include <bits/stdc++.h>
#define loop(n) for (lint ngtkana_is_a_genius = 0; ngtkana_is_a_genius < lint(n); ngtkana_is_a_genius++)
#define rep(i, begin, end) for (lint i = lint(begin); (i) < lint(end); i++)
#define all(v) v.begin(), v.end()
#define rand(l, r) std::uniform_int_distribution<>(l, r)(mt)
using lint = long long;
auto mt = std::mt19937_64(std::random_device{}());
auto cmn = [](auto& a, auto b){ if (a > b) {a = b; return true;} return false; };
auto cmx = [](auto& a, auto b){ if (a < b) {a = b; return true;} return false; };
void debug_impl() { std::cerr << std::endl; }
template <typename Head, typename... Tail>
void debug_impl(Head head, Tail... tail) { std::cerr << " " << head; debug_impl(tail...); }
#ifndef STOPIT
#define debug(...)\
	do {\
		std::cerr << std::boolalpha << "[" << #__VA_ARGS__ << "]:";\
		debug_impl(__VA_ARGS__);\
		std::cerr << std::noboolalpha;\
	} while (false)
#else
#define debug(...) {}
#endif

template < typename Container, typename Value = typename Container::value_type, std::enable_if_t<!std::is_same< Container, std::string >::value, std::nullptr_t> = nullptr>
std::istream& operator>> (std::istream& is, Container& v)
	{ for (auto & x : v) { is >> x; } return is; }

template < typename Container, typename Value = typename Container::value_type, std::enable_if_t<!std::is_same< Container, std::string >::value, std::nullptr_t> = nullptr >
std::ostream& operator<< (std::ostream& os, Container const& v) {
 os << "{";
	for (auto it = v.begin(); it != v.end(); it++)
		{os << (it != v.begin() ? "," : "") << *it;}
	return os << "}";
}

template < template < typename ... > class Tuple,  typename... Args, std::size_t ... Inds, std::size_t = std::tuple_size< Tuple < Args ... > >::value >
std::istream& tuple_input_impl(std::istream& os, Tuple<Args...>& tuple, std::integer_sequence<std::size_t, Inds...>)
	{ (void)std::initializer_list<int>{((void)(os >> std::get< Inds >(tuple)), 0)...}; return os; }
template < template < typename ... > class Tuple,  typename... Args, std::size_t = std::tuple_size< Tuple < Args ... > >::value >
std::istream& operator>> (std::istream& os, Tuple<Args...>& tuple)
	{ return tuple_input_impl(os, tuple, std::index_sequence_for<Args...>()); }

template < template < typename ... > class Tuple,  typename... Args, std::size_t ... Inds, std::size_t = std::tuple_size< Tuple < Args ... > >::value >
std::ostream& tuple_output_impl(std::ostream& os, const Tuple<Args...>& tuple, std::integer_sequence<std::size_t, Inds...>)
	{ os << "("; (void)std::initializer_list<int>{((void)(os << (Inds > 0 ? "," : "") << std::get< Inds >(tuple)), 0)...}; return os << ")"; }
template < template < typename ... > class Tuple,  typename... Args, std::size_t = std::tuple_size< Tuple < Args ... > >::value >
std::ostream& operator<< (std::ostream& os, const Tuple<Args...>& tuple)
 { return tuple_output_impl(os, tuple, std::index_sequence_for<Args...>()); }

template < class Container, class Value = typename Container::value_type >
auto run_length(Container const& v) {
	auto n = (int)v.size();
	if (n == 0)
		{ return std::vector< std::pair< Value, int > >{}; }
	auto pos = std::vector< int >{};
	for (auto i = 1; i < n; i++) {
		if (v.at(i - 1) != v.at(i))
			{ pos.emplace_back(i); }
	}
	pos.emplace_back(n);
	auto m = (int)pos.size();
	auto len = std::vector< int >(m);
	std::adjacent_difference(pos.begin(), pos.end(), len.begin());
	auto ret = std::vector< std::pair< Value, int > >(m);
	for (auto i = 0; i != m; i++)
		{ ret.at(i) = {v.at(pos.at(i) - 1), len.at(i)}; }
	return ret;
}

void err() { std::cout << 0 << std::endl; exit(0); }
#define require(exp) do { if (!(exp)) { err(); } } while(false)

int main() {
	std::cin.tie(0); std::cin.sync_with_stdio(false);
	int n; std::cin >> n;
	std::vector<lint> a(n); std::cin>>a;
	std::sort(all(a));
	auto rle = run_length(a);
	debug(rle);

	lint x = -1, y = -1, z = -1;
	for (auto&& pair : rle) {
		lint val, pos; std::tie(val, pos) = pair;
		if (pos < 2) continue;
		if (4 <= pos) x = val;
		y = z;
		z = val;
	}
	debug(x,y,z);

	lint ans = 0;
	if (x != -1) {
		cmx(ans, x * x);
	}
	if (y != -1 && z != -1) {
		assert(y < z);
		cmx(ans, y * z);
	}
	std::cout << ans << std::endl;
	return 0;
}

Measured memory_bytes: 3576