#include <bits/stdc++.h>

using namespace std;
vector<int> v;

long long subar(int st, int ed)
{
    long long rez = 0;
    for(int i = st; i <= ed; ++i)
        for (int j = i + 1; j <= ed; ++j)
            rez += (long long)v[i] * (long long)v[j];
    return rez;
}

int main()
{
    int N;
    cin >> N;
    v.push_back(0);
    for (int i = 1 ; i <= N; ++i) {
        int x;
        cin >> x;
        v.push_back(x);
    }

    long long best = -(1<<62);
    for (int i = 1; i <= N; ++i)
        for (int j = 1; j <= N; ++j)
            best = max(best, subar(i, j));

    cout << best << "\n";

    return 0;
}