#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;

int main()
{
        ll N; cin >> N;
        vector<ll> A(N, 0);
        map<ll, ll, greater<ll>> m;
        for (int i = 0; i < N; ++i) {
                cin >> A[i];
                m[A[i]]++;
        }
        int cnt = 0;
        ll a = 0;
        ll b = 0;
        for (auto i : m) {
                if (i.second > 1) {
                        if (cnt == 0) {
                                a = i.first;
                                if (i.second > 3) {
                                        b = i.first;
                                        break;
                                }
                                cnt++;
                        }
                        else {
                                b = i.first;
                                break;
                        }
                }
        }
        cout << a * b << endl;



}

#include <bits/stdc++.h>
  
using namespace std;
  
template<class T> void ckmin(T &a, T b) { a = min(a, b); }
template<class T> void ckmax(T &a, T b) { a = max(a, b); }
  
#define pb push_back
#define mp make_pair
#define cotu cout
#define itn int
#define Red ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0)
#define F first
#define S second
#define sz(x) (int)x.size()
#define all(x) (x).begin(), (x).end()
#define rep(i, n) for(int i = 0; i < n; ++i)
#define repr(i,n) for(int i = n - 1; i >= 0; --i)
#define Rep(i, a, n) for(int i = (a); i <=(n); ++i)
#define repst(i, n) for(auto it = n.begin(); it != n.end(); ++it)
#define Repr(i, a, n) for(int i = (n); i >= (a); --i)
#define sp(x) fixed << setprecision(x)
#define ordered_set tree<int , null_type,less<int >, rb_tree_tag,tree_order_statistics_node_update> 
  
#include <ext/pb_ds/assoc_container.hpp> 
#include <ext/pb_ds/tree_policy.hpp> 
using namespace __gnu_pbds; 
  
typedef long long ll;
typedef pair<ll, ll> pll;
typedef pair<int, int> pii;
  
const int inf = int(1e9);
const int mod = inf + 7;
const int N = 1e6 + 555; // TL MB
const double PI = acos(-1.0);
void mul(ll &x, ll y){
	x *= y;
	if(x >= mod) x %= mod;
}
 
void add(ll &x, ll y){
	x += y;
	if(x >= mod) x -= mod;
	if(x < 0) x += mod;
}
ll bp(ll a, ll n){
	ll r = 1;
	while(n){
		if(n & 1) mul(r, a);
		mul(a, a);
		n >>= 1;
	}
 
}



void solve()
{
	int n;
	cin >> n;
	ll a[n];
	vector<ll> p;
	rep(i, n) cin >> a[i];
	sort(a, a + n);
	rep(i, n){
		if(i && a[i] == a[i - 1]) p.pb(a[i++]);
	}
	sort(p.rbegin(), p.rend());
	if(sz(p) <= 1) cout << 0;
	else cout << p[0] * p[1];
}

 
int main()
{
	// freopen("crosses.in", "r", stdin);
	// freopen("crosses.out", "w", stdout);
    Red;
  	int T = 1;
  	// cin >> T;
  	for(int i = 1; i <= T; ++i){
  		solve();
  	}
  	return 0;

}