#include <bits/stdc++.h>

using namespace std;

long calculateVal(vector<int>A , int s,int e) 
{
    long value  = 0;
   for(int i = s;i<e-1;i++) {
        for(int j = i+1;j<e;j++) {
            value+=(A[i]*A[j]);
        }
    }
    return value;
}

long largestValue(vector <int> A) {
    int s = A.size();
    long value = 0;
    int tem = 0;
    for(int i = 0;i<s-1;i++) {
        for(int j = i+1;j<s;j++) {
           long temp = calculateVal(A,i,j);
            if(tem == 0){value = temp;tem++;}
            else if(temp>value)value = temp;
        }
    }
    return value;
    // 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);
    cout << result << endl;
    return 0;
}