#include <bits/stdc++.h>
using namespace std;

long long main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    long long n; cin >> n;
    map<long long, long long> m;
    vector<long long> v(0);
    for (long long i = 0; i < n; i++)
    {
        long long be; cin >> be;
        m[be]++;
        if (m[be] == 2)
        {
            v.push_back(be);
        }
    }
    
    sort(v.begin(), v.end());
    if (v.size() > 0 && m[v.size()-1] > 3)
    {
        cout << v[v.size()-1] * v[v.size()-1] << endl;
    }
    else
    {
        if (v.size() > 1)
        {
            cout << v[v.size()-1] * v[v.size()-2] << endl;
        }
        else
        {
            cout << "0" << endl;
        }
    } 
    return 0;
}