#include <bits/stdc++.h>

using namespace std;

long largestValue(vector <int>& A) {
    // Return the largest value of any of A's nonempty subarrays.
    long ans = 0;
    int len = A.size();
    for (int start = 0; start < len - 1; start++) {
        for (int end = start + 1; end <= len - 1; end++) {
            long sum = 0;
            for (int i = start; i < end; i++) 
                for (int j = i + 1; j <= end; j++)
                    sum += A[i] * A[j];
            ans = max(ans, sum);
        }
    }
    return ans;
}

int main() {
    int n;
    cin >> n;
    vector<int> A(n);
    for(int A_i = 0; A_i < n; A_i++){
       cin >> A[A_i];
    }
    long result = largestValue(A);
    cout << result << endl;
    return 0;
}