#include <bits/stdc++.h>

using namespace std;

long largestValue(vector <int> A, int n) {
    long temp1 = 0, temp2 = 0,amx = 0;
    for(int i=0;i<n;i++)
    {
        temp1 = 0; temp2 = 0;
        for(int j=i;j<n;j++)
        {
           // cout<<"i is : "<<i<<" and j is : "<<j<<" max is "<<amx<<endl;
            temp1+=A[j];
            temp2+=A[j]*A[j];
            /*for(int k = i;k<=j;k++)
            {
                
                temp1+=A[k];
                temp2+=A[k]*A[k];
            }*/
                long temp4 = temp1*temp1;
                long temp3 = (temp4 - temp2)/2;
                if(amx<temp3)
                    amx = temp3;
        }
    }
    return amx;
    // Return the largest value of any of A's nonempty subarrays.
}

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,n);
    cout << result << endl;
    return 0;
}