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

using namespace std;

#define pb push_back

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

#define rep1(i,n) for(int i=1;i<=n;i++)

#define mp make_pair

#define F first

#define S second

#define IOS ios_base::sync_with_stdio(0); cin.tie(0)

typedef long long ll;

vector<int> g[100005];

ll q,n;

ll a[1005];

int main()

{

    //IOS;

    while(cin>>n)

    {

        map<ll,ll> m;

        vector<ll> ans;

        rep(i,n)

        {

            ll tmp;

            cin>>tmp;

            m[tmp]++;

            if(m[tmp]%2==0) ans.pb(tmp);

        }

        sort(ans.begin(),ans.end());

        if(ans.size()<2) cout<<0<<"\n";

        else cout<<ans[ans.size()-1]*ans[ans.size()-2]<<"\n";

    }

    return 0;

}




// Faster C++ solution for the same problem (measured speedup: 3.503906135976655x):
///Bismillahir Rahmanir Rahim

///ALLAHU AKBAR

#include<bits/stdc++.h>

#define flash() ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);



#define sc1i(a) scanf("%d",&a)

#define sc2i(a,b) scanf("%d %d",&a,&b)

#define   sc3i(a,b,c)       scanf("%d %d %d",&a, &b, &c)

#define    p1i(a)           printf("%d\n",(a))

#define    p2i(a,b)        printf("%d %d\n",(a), (b))

#define    p3i(a,b,c)      printf("%d %d %d\n",(a), (b), (c))





#define sc1l(a) scanf("%lld",&a)

#define sc2l(a,b) scanf("%lld %lld",&a,&b)

#define   sc3l(a,b,c)       scanf("%lld %lld %lld",&a, &b, &c)

#define    p1l(a)           printf("%lld\n",(a))

#define    p2l(a,b)        printf("%lld %lld\n",(a), (b))

#define    p3l(a,b,c)      printf("%lld %lld %lld\n",(a), (b), (c))





#define c(x)       cout<<x<<endl

#define cy  cout<<"YES"<<endl

#define cn   cout<<"NO"<<endl

#define f1(i,a,b)  for(ll i=a;i<b;i++)

#define f2(i,a,b) 	for(ll i=a;i<=b;i++)

#define fr(i,a,b)   for(ll i=a;i>=b;i--)

#define LCM(a,b)                (a / __gcd(a,b) ) *b

#define GCD(a,b)                __gcd(a,b)

#define dist(x1,y1,x2,y2)       sqrt((x2-x1)*(x2-x1) + (y2-y1)*(y2-y1))

#define distl(x1,y1,x2,y2)      sqrtl((x2-x1)*(x2-x1) + (y2-y1)*(y2-y1))



#define geta(a,n)           for(int i=0;i<n;i++) cin>>a[i]

#define puta(a,n)           for(int i=0;i<n;i++) cout<<a[i]<<" "



#define geta1(a,n)           for(int i=1;i<=n;i++) cin>>a[i]

#define puta1(a,n)           for(int i=1;i<=n;i++) cout<<a[i]<<" "





#define getar(a,n)           for(int i=0;i<n;i++) scanf("%lld",&a[i])

#define getar1(a,n)           for(int i=1;i<=n;i++) scanf("%lld",&a[i])

#define putar(a,n)           for(int i=0;i<n;i++) printf("%lld ",a[i])

#define putar1(a,n)           for(int i=1;i<=n;i++) printf("%lld ",a[i])

#define all(a)                  a.begin(),a.end()

#define lla(A)                  A.rbegin(), A.rend()

#define unique(a)               sort(all(a)),a.erase(unique(all(a)),a.end())

#define pb                      push_back

#define mk                      make_pair

#define ff                      first

#define ss                      second

#define greatersrt(v)  sort(v.begin(),v.end(),greater<ll>())

#define min3(a,b,c)             min(a,min(b,c))

#define min4(a,b,c,d)           min(a,min(b,min(c,d)))

#define max3(a,b,c)             max(a,max(b,c))

#define max4(a,b,c,d)           max(a,max(b,max(c,d)))

#define max5(a,b,c,d,e)         max(max3(a,b,c),max(d,e))

#define min5(a,b,c,d,e)         min(min3(a,b,c),min(d,e))

#define mem(a,x)                memset(a,x,sizeof(a))

#define see_you                     return 0

#define sorta(a,n)                   sort(a,a+n)

#define SORT(v)                 sort(v.begin(),v.end())

#define REV(v)                  reverse(v.begin(),v.end())

#define gp ' '

#define nl                        printf("\n")

int caseno=0;



#define  printcase             printf("Case %d: ",++caseno)

#define Debug                   cout<<endl<<"AND I AM IRONMAN"<<endl;

#define binleastsigonebit(x)    __builtin_ffs(x)

#define binleadingzeroes(x)     __builtin_clz(x)

#define bintrailingzeroes(x)    __builtin_ctz(x)

#define bintotalones(x)         __builtin_popcount(x)



//Datatypes

#define ll                      long long

#define ULL                     unsigned long long

#define LD                      long double

#define UI                      unsigned int

#define US                      unsigned short

#define pii             pair<int,int>

#define pll             pair<ll,ll>





//Constants

const int MOD = 1000000007; // 998244353

const ll INF = 1e18;

const ll inf = 0xFFFFFFFFFFFFFFFL;

const int maxn = 211111;

const int N = 1111111;

#define PI                      acos(-1.0)

#define EulerGamma              0.57721566490153286060651209





//ll powmod(ll base, ll power) { if (power == 0) return 1; else {ll cur = powmod(base, power / 2); cur = cur * cur; cur = cur % MOD;if (power % 2 == 1) cur = cur * base; cur = cur % MOD; return cur;}





/*------------------------------Graph Moves----------------------------*/

//const int fx[]={+1,-1,+0,+0};

//const int fy[]={+0,+0,+1,-1};

//const int fx[]={+0,+0,+1,-1,-1,+1,-1,+1};   // Kings Move

//const int fy[]={-1,+1,+0,+0,+1,+1,-1,-1};  // Kings Move

//const int fx[]={-2, -2, -1, -1,  1,  1,  2,  2};  // Knights Move

//const int fy[]={-1,  1, -2,  2, -2,  2, -1,  1}; // Knights Move

/*---------------------------------------------------------------------*/

///ceil(x/y)==(x+y-1)/y





using namespace std;

#include <ext/pb_ds/assoc_container.hpp>

#include <ext/pb_ds/tree_policy.hpp>

using namespace __gnu_pbds;

#define ordered_set tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update>



//from a loser

ll a[maxn];



int main()

{

    flash()

    ll i,j,t,cas=0;

    ll n;cin>>n;

    f1(i,0,n) cin>>a[i];

    sort(a,a+n);



    ll x=0,y=0,a1=0,b1=0,c1=0;

    for(i=n-1;i>=0;i--)

    {

        if(a[i]==a[i-1] and a1==0)

        {

            a1=a[i];i--;

        }

        else if(a[i]==a[i-1] and b1==0)

        {

            b1=a[i];i--;

        }

    }

    //cout<<a1<<" "<<b1<<endl;

    x=a1*b1;



    for(i=n-1;i>=0;i--)

    {

        if(a[i]==a[i-1] and a[i-1]==a[i-2] and a[i-2]==a[i-3] and c1==0)

        {

            c1=a[i];

        }

    }

   // cout<<c1<<endl;

    y=c1*c1;

    cout<<max(x,y)<<endl;





    see_you;

}