// __author__ HD

#include <bits/stdc++.h>

#define endl '\n'
#define MAX 100005
#define MOD 1000000007
using namespace std;

typedef long long ll;

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);

    // Solve

    ll solve = 0;

    ll n;
    vector<ll> array;
    cin >> n;
    array.assign(n, 0);
    for (int i = 0; i < n; ++i) {
        cin >> array[i];
    }

    for (int i = 0; i < n; ++i) {
        for (int j = i+1; j < n; ++j) {
            ll aux = 0;
            for (int k = i; k < j; ++k) {
                for (int l = k+1; l < j+1; ++l) {
                    aux += array[k]*array[l];
                }
            }
            if(aux > solve)
                solve = aux;
        }
    }
    
    cout << solve << endl;
    
    return 0;
}