#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
#include "debug.h"
#else
#define dump(...)
#endif
#define endl "\n"
#define ll long long
#define FOR(i, a, b) for (int i = (int)(a); i < (int)(b); i++)
#define REP(i, x) for (int i = 0; i < (int)(x); i++)
#define REPS(i, x) for (int i = 1; i <= (int)(x); i++)
#define RREP(i, x) for (int i = ((int)(x)-1); i >= 0; i--)
#define RREPS(i, x) for (int i = ((int)(x)); i > 0; i--)
#define INF 2147483647
#define LLINF 9223372036854775807LL
#define vi vector<int>
#define vvi vector<vector<int>>
#define pi pair<int, int>
#define ALL(a) (a).begin(), (a).end()
#define BIT(n) (1LL << (n))
#define UNIQUE(v) v.erase(unique(v.begin(), v.end()), v.end()) //sortしてからつかうこと
constexpr ll MOD = 1e9 + 7;
int dx[8] = {1, 0, -1, 0, 1, 1, -1, -1};
int dy[8] = {0, 1, 0, -1, 1, -1, 1, -1};
ll A, B, C, D, E, F, G, H, N, M, L, K, P, Q, R, W, X, Y, Z;
string S, T;
ll ans = 0;

template <typename T>
istream &operator>>(istream &is, vector<T> &vec) {
    for (T &x : vec)
        is >> x;
    return is;
}

int intceil(int a, int b) {
    return (a + (b - 1)) / b;
}

signed main() {
    cin >> N;
    vi a(N);
    cin >> a;
    map<int, int> mp;
    vector<ll> v;
    REP(i, N) {
        int x = ++mp[a[i]];
        if ((x & 1) == 0) {
            v.push_back(a[i]);
        }
    }
    sort(v.rbegin(), v.rend());
    if (v.size() >= 2)
        cout << (ll)v[0] * (ll)v[1] << endl;
    else
        cout << 0 << endl;
}
#define _GLIBCXX_DEBUG
#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for (int i = 0;i < (n);i++)
using ll = long long;
const ll MOD=1000000007;



int main() 
{
  ll N; cin>>N;
  vector<ll> vecA(N);
  rep(i,N)
  {
    cin>>vecA.at(i);
  }
  sort(vecA.begin(),vecA.end());
  reverse(vecA.begin(),vecA.end());
  ll L=0;
  rep(i,N-1)
  {
    if(vecA.at(i)==vecA.at(i+1))
    {
      if(L==0) {L=vecA.at(i); i++; continue;}
      cout<<L*vecA.at(i)<<endl; return 0;
    }
  } 
  cout<<0<<endl;
  return 0;
}