// Slower C++ solution:
#include<bits/stdc++.h>

using namespace std;



#define LL long long

#define LD long double

#define Mod 1000000007

#define L_Mod 17100000013



const double eps = 1e-9;

const int INF = 0x3f3f3f3f;

const double PI = 3.1415926535;



#define NO_TLE std::ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);



#define ree(a,n) memset(a,n,si 2)



#define rep(i,n) for(int (i)=0;(i)<(int)(n);++(i))

#define rer(i,l,u) for(int (i)=(int)(l);(i)<=(int)(u);++(i))

#define red(i,l,u) for(int (i)=(int)(l);(i)>=(int)(u);--(i))

int main()

{

    LL int i,j,n,m,a[100002]= {0};

    cin>>n;

    for(i=0; i<n; i++)

        cin>>a[i];

    sort(a,a+i,greater<int>());

    LL int ma=0,num=0;

    for(i=0; i<n-1; i++)

    {

        if(a[i]==a[i+1])

        {

            if(num==0)

                ma=a[i];

            else

                ma*=a[i];

            num++;

            i++;

        }

        if(num>=2)

            break;

    }

    if(num>=2)

        cout<<ma;

    else

        cout<<0;

}


// Faster C++ solution for the same problem (measured speedup: 1.7483650672198685x):
/*بِسْمِ اللَّهِ الرَّحْمَنِ الرَّحِيم*/



//#pragma GCC optimize("O3,unroll-loops")

//#pragma GCC target("avx,avx2,fma")



#include <bits/stdc++.h>

using namespace std;

#define FASTIO ios_base::sync_with_stdio(false), cin.tie(0), cout.tie(0);

typedef long long ll;

const double PI = acos(-1.0);

const ll mod = 1e9 + 7;

//const ll mod = 998244353;





inline void normal(ll &a) { a %= mod; (a < 0) && (a += mod); }

inline ll modMul(ll a, ll b) { a %= mod, b %= mod; normal(a), normal(b); return (a * b) % mod; }

inline ll modAdd(ll a, ll b) { a %= mod, b %= mod; normal(a), normal(b); return (a + b) % mod; }

inline ll modSub(ll a, ll b) { a %= mod, b %= mod; normal(a), normal(b); a -= b; normal(a); return a; }

inline ll modPow(ll b, ll p) { ll r = 1; while (p) { if (p & 1) r = modMul(r, b); b = modMul(b, b); p >>= 1; } return r; }

inline ll modInverse(ll a) { return modPow(a, mod - 2); }

inline ll modDiv(ll a, ll b) { return modMul(a, modInverse(b)); }



#define si(x) scanf("%d",&x)

#define sii(x,y) scanf("%d %d",&x,&y)

#define siii(x,y,z) scanf("%d %d %d",&x,&y,&z)

#define sl(x) scanf("%lld",&x)

#define sll(x,y) scanf("%lld %lld",&x,&y)

#define slll(x,y,z) scanf("%lld %lld %lld",&x,&y,&z)

#define ss(ch) scanf("%s",ch)

#define pi(x) printf("%d",x)

#define pii(x,y) printf("%d %d",x,y)

#define piii(x,y,z) printf("%d %d %d",x,y,z)

#define pl(x) printf("%lld",x)

#define pll(x,y) printf("%lld %lld",x,y)

#define plll(x,y,z) printf("%lld %lld %lld",x,y,z)

#define ps(ch) printf("%s",ch)

#define F(i,a,b)      for(int i= a; i <= b; i++)

#define R(i,b,a)      for(int i= b; i >= a; i--)



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

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

int dx8[] = {0, 0, 1, 1, 1, -1, -1, -1};

int dy8[] = {1, -1, -1, 0, 1, -1, 0, 1};

int kx8[] = {1, 1, 2, 2, -1, -1, -2, -2};

int ky8[] = {2, -2, 1, -1, 2, -2, 1, -1};

/* for Random Number generate

mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

*/

///**

template < typename F, typename S >ostream& operator << ( ostream& os, const pair< F, S > & p ) {return os << "(" << p.first << ", " << p.second << ")";}

template < typename T >ostream &operator << ( ostream & os, const vector< T > &v ) {os << "{"; for (auto it = v.begin(); it != v.end(); ++it) {if ( it != v.begin() ) os << ", "; os << *it;} return os << "}";}

template < typename T >ostream &operator << ( ostream & os, const set< T > &v ) {os << "["; for (auto it = v.begin(); it != v.end(); ++it) {if ( it != v.begin()) os << ", "; os << *it;} return os << "]";}

template < typename F, typename S >ostream &operator << ( ostream & os, const map< F, S > &v ) {os << "["; for (auto it = v.begin(); it != v.end(); ++it) {if ( it != v.begin() ) os << ", "; os << it -> first << " = " << it -> second ;} return os << "]";}

#define dbg(args...) do {cerr << #args << " : "; faltu(args); } while(0)

clock_t tStart = clock();

#define timeStamp dbg("Execution Time: ", (double)(clock() - tStart)/CLOCKS_PER_SEC)

void faltu () { cerr << endl; }

template <typename T>void faltu( T a[], int n ) {for (int i = 0; i < n; ++i) cerr << a[i] << ' '; cerr << endl;}

template <typename T, typename ... hello>

void faltu( T arg, const hello &... rest) { cerr << arg << ' '; faltu(rest...); }



// Program showing a policy-based data structure.

#include <ext/pb_ds/assoc_container.hpp> // Common file 

#include <ext/pb_ds/tree_policy.hpp>

#include <functional> // for less 

using namespace __gnu_pbds;



// GNU link : https://goo.gl/WVDL6g

typedef tree<int, null_type, less_equal<int>, rb_tree_tag,

        tree_order_statistics_node_update>

        new_data_set;

// find_by_order(k) – ফাংশনটি kth ordered element এর একটা পয়েন্টার রিটার্ন করে। অর্থাৎ তুমি চাইলেই kth ইন্ডেক্সে কি আছে, সেটা জেনে ফেলতে পারছো!

// order_of_key(x) – ফাংশনটি x এলিমেন্টটা কোন পজিশনে আছে সেটা বলে দেয়।

//*//**___________________________________________________**/

const int N = 1000006;





int main()

{

  FASTIO

  /*

#ifndef ONLINE_JUDGE

  freopen("in.txt", "r", stdin);

  freopen("out.txt", "w", stdout);

  freopen("error.txt", "w", stderr);

#endif

//*/

  int T;

  T = 1;

  //scanf("%d", &T);

  for (int cs = 1; cs <= T; cs++) {

    ll n;

    cin >> n;

    vector<ll> a(n);

    map<ll, ll>mp;

    ll ans = 0;

    for (auto &x : a) {

      cin >> x;

      mp[x]++;

    }

    sort(a.rbegin(), a.rend());

    for (int i = 0; i < n; i++) {

      if (mp[a[i]] >= 4) {

        ans = max(ans, a[i] * a[i]);

        cout << ans << "\n";

        return 0;

      }

      else if (mp[a[i]] >= 2) {

        for (int j = i + 1; j < n; j++) {

          if (a[i] == a[j])continue;

          if (mp[a[j]] >= 2) {

            ans = max(ans, a[i] * a[j]);

            cout << ans << "\n";

            return 0;

          }

        }

      }

    }



    cout << ans << "\n";

  }

  return 0;

}