#include <iostream>
#include <vector>
#include <algorithm>
#include <map>
#include <cstdint>
using namespace std;
typedef int64_t ll;

int main() {
    ll n;
    cin >> n;
    map<ll,ll> mp;
    for(ll i = 0; i < n; i++) {
        ll tmp;
        cin >> tmp;
        mp[tmp]++;
    }

    /*
    for(const auto & x : mp) {
        cerr << "\nmp " << x.first << " = " << x.second; 
    }
    */

    ll a = 0, b = 0;
    for(auto it = mp.rbegin(); it != mp.rend(); it++) {
        auto x = *it;
        //cerr << "\nx=" << x.first;
        if(x.second < 2) {
            //cerr << "\nskipped";
            continue;
        }
        if(x.second >= 2 && x.second < 4) {
            if(a == 0) {
                a = x.first;
            }else{
                b = x.first;
                break;
            }
        }
        if(x.second >= 4) {
            if(a == 0) {
                a = x.first;
                b = x.first;
            }else{
                b = x.first;
            }
            break;
        }
    }
    cout << a * b;
}