#include <bits/stdc++.h>

#define F first
#define S second
#define MP make_pair
#define pb push_back
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define LCM(a, b) (a) / __gcd((a), (b)) * (b)
#define CEIL(a, b) (a)/(b)+(((a)%(b))?1:0)
#define ln '\n'

using namespace std;
using LL = long long;
using ldouble = long double;
using P = pair<int, int>;
using LP = pair<LL, LL>;

static const int INF = INT_MAX;
static const LL LINF = LLONG_MAX;
static const int MIN = INT_MIN;
static const LL LMIN = LLONG_MIN;
static const int MOD = 1e9 + 7;
static const int SIZE = 200005;

const int dx[] = {0, -1, 1, 0};
const int dy[] = {-1, 0, 0, 1};

vector<LL> Div(LL n) {
    vector<LL> ret;
    for(LL i = 1; i * i <= n; ++i) {
        if(n % i == 0) {
            ret.pb(i);
            if(i * i != n) ret.pb(n / i);
        }
    }
    sort(all(ret));
    return ret;
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);

    int N;
    cin >> N;
    vector<int> v(N);
    for(int i = 0; i < N; ++i) {
        cin >> v[i];
    }
    sort(all(v));

    LL a, b;
    a = 0, b = 0;
    for(int i = 0; i < N - 1; ++i) {
        if(v[i] == v[i + 1]) {
            b = a;
            a = v[i];
            i++;
        }
    }
    cout << a * b << endl;

    return 0;
}

#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < n; i++)
typedef long long ll;
using namespace std;

int main() {
    int n;
    cin >> n;
    map<ll, int, greater<ll>> m;
    rep(i, n) {
        ll a;
        cin >> a;
        m[a]++;
    }

    int cnt = 0;
    ll ans = 0;
    for (auto e : m) {
        if (e.second >= 4 && cnt == 0) {
            ans = e.first * e.first;
            cnt += 2;
            break;
        } else if (e.second >= 2) {
            if (cnt == 0)
                ans = e.first, cnt++;
            else if (cnt == 1) {
                ans *= e.first, cnt++;
                break;
            }
        }
    }

    if (cnt == 1) ans = 0;
    cout << ans << endl;
    return 0;
}
