    /**   Created by: Marcos Portales
          Codeforces User: marcosportales
          Country: Cuba
          Copyright                    */
#include<bits/stdc++.h>
using namespace std;
/// Pragmas:
#pragma GCC optimize("Ofast","unroll-loops","omit-frame-pointer","inline") //Optimization flags
#pragma GCC option("arch=native","tune=native","no-zero-upper") //Enable AVX
#pragma GCC target("avx2") //Enable AVX
/// Macros:
#define int long long
#define f first
#define s second
#define db(x) cerr << #x << ": " << (x) << '\n';
#define pb push_back
#define lb lower_bound
#define up upper_bound
#define all(x) x.begin() , x.end()
#define rall(x) x.rbegin() , x.rend()
#define enl '\n'
#define vi vector<int>
#define sz(a) int((a).size())
#define rep(i,n) for(int i=0;i<(n);i++)
#define repi(i,n) for(int i=(1);i<=(n);i++)
typedef pair<int,int> ii;
typedef long double ld;
typedef unsigned long long ull;
/// Constraints:
const int maxn = 200005;
const int mod = 1000000007;
const ld eps = 1e-9;
const int inf = ((1ll<<31ll)-1ll);
const int INF = 2000000000000000000ll;
const ld pi = acos(-1);
/// Prime Numbers:
// 2, 173, 179, 181, 197, 311, 331, 737, 1009, 2011, 2027, 3079, 4001, 10037, 10079, 20011, 20089;
// 100003, 100019, 100043, 200003, 200017, 1000003, 1000033, 1000037, 1000081;
// 2000003, 2000029, 2000039, 1000000007, 1000000021, 2000000099;
/// Functions:
#define lg2(x) 31 - __builtin_clz(x)
#define lgx(x,b) ( log(x) / log(b) )
/// Red-Black Tree Test.insert(x)late ---------------------------------
//#include <ext/pb_ds/assoc_container.hpp>
//#include <ext/pb_ds/tree_policy.hpp>
//using namespace __gnu_pbds;
//typedef tree < long long ,  null_type ,  less<long long> ,  rb_tree_tag ,  tree_order_statistics_node_update > ordered_set;
/// Quick Pow------------------------------------------------
int qpow(int b,int e){
    if( !e ) return 1;
    if( e & 1 ) return qpow(b,e-1) * b % mod;
    int pwur = qpow(b,e>>1);
    return (pwur * pwur) % mod;
}
int modinv(int x){
    return qpow(x,mod-2);
}

/// My Code -------------------------------------------------

int32_t main(){
    ios_base::sync_with_stdio(0); cin.tie(0);
    cout.setf(ios::fixed); cout.precision(0);
    srand(time(NULL));
    //freopen("a.in","r",stdin);
    //freopen("a.in","w",stdout);
    int n;
    cin>>n;
    vi v(n);
    rep(i,n)cin>>v[i];
    sort(rall(v));
    int ans=1,cnt=0;
    for(int i=0;i<n-1;){
        if(v[i]==v[i+1]&&cnt<2){
            ans*=v[i];
            i+=2;
            cnt++;
        }
        else i++;
    }
    if(cnt==2)cout<<ans;
    else cout<<0;
    return 0;
}

#include<bits/stdc++.h>
#define rep(i,N) for(int i=0;i<(N);i++)
#define FOR(i,a,b) for(int i=(a);i<(b);i++)
using namespace std;
const long long MOD = 1e9 + 7;
const long long INF = 1e12;
const int inf = 1e9;
const int mod = 1e9+7;
typedef long long ll;
typedef pair<ll,int> P;
typedef set<int> S;
int main(){
    cout << fixed << setprecision(10);
    int n;
    cin >> n;
    map<ll,int> mli;
    rep(i,n){
        ll x;
        cin >> x;
        mli[x]++;
    }
    vector<pair<ll,int>> v;
    for(auto u : mli){
        v.push_back({u.first,u.second});
    }
    sort(v.begin(),v.end());
    reverse(v.begin(),v.end());
    ll ans = 1;
    bool one = 0;
    for(auto u : v){
        if(u.second>=2){
            if(u.second>=4){
                if(one) cout << ans*u.first << endl;
                else cout << u.first*u.first << endl;
                return 0;
            }
            else{
                if(one) {
                    cout << ans*u.first << endl;
                    return 0;
                }
                else ans *= u.first;
            }
            one = 1;
        }
    }
    cout << 0 << endl; 
    return 0;
}