#include<bits/stdc++.h>
using namespace std;
struct p
{
	long long int a,b;
};
int main()
{
	long long int n;
	cin>>n;
	vector<long long int> v;
	for (long long int i=0;i<n;i++)
	{
		long long int n1;
		cin>>n1;
		v.push_back(n1);
	}
	vector<struct p> v1;
	for (long long int i=0;i<n;i++)
	{
		for (long long int j=i+1;j<n;j++)
		{
			struct p k;
			k.a=v[i];
			k.b=v[j];
			v1.push_back(k);
		}
	}
	vector<long long int> v2;
	for (long long int i=0;i<v1.size();i++)
	{
        long long int p1=0;
        for (long long int j=0;j<=i;j++)
        {long long int pr=1;
		pr=v1[j].a*v1[j].b;
		p1=p1+pr;}
        v2.push_back(p1);
	}
    sort(v2.begin(),v2.end());
    cout<<v2[v2.size()-1];
	//cout<<p1;
	return 0;
}