#include <bits/stdc++.h>
#define IOS ios_base::sync_with_stdio(false); cin.tie(0);
using namespace std;

int main(){
//	IOS;
	int n,inp;
	cin >> n;
	map<int,int> num;
	vector<int> can;
	for(int i=0;i<n;i++){
		cin >> inp;
		num[inp]++;
		if(num[inp]%2==0) can.push_back(inp);
	}
	sort(can.begin(),can.end(),greater<int>());
	if(can.size()<2) cout << "0\n";
	else cout << (long long int)can[0]*can[1] << '\n';
	return 0;
}
