#include <bits/stdc++.h>

using namespace std;

#define ll long long 

ll N = 1e5+5;
vector<ll> ar(N);

ll pair_sum(ll l, ll r){
    ll sum = 0;
    for (int i = l; i < r; ++i)
    {
        for(int j = i+1; j < r; j++){
            sum += ar[i]*ar[j];
        }
    }
    return sum;
}

void compute(ll n) {
    // Complete this function
    ll N = n;
    ll maxi = 0;
    for (ll i = 0; i < N; ++i)
    {
        for (ll j = i+1; j < N; ++j)
        {
            maxi = max(maxi, pair_sum(i,j));
        }
    }

    cout << maxi << endl;
}

int main() {
    ll n;
    cin >> n;
    for(ll a0 = 0; a0 < n; a0++){
        cin >> ar[a0];
    }
    compute(n);
    return 0;
}