#include <math.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <assert.h>
#include <limits.h>
#include <stdbool.h>

int first_sum (int *A,int start_pos,int a_size){
    int i = 0,j=0;
    int ind_sum = 0;
    for(i=start_pos;i<a_size-start_pos;i++){
        for(j=i+1;j<a_size-start_pos;j++){
         ind_sum = ind_sum +  (A[i]*A[j]);  
        }
      
    }
   // printf("frist sum [%d]\n",ind_sum);
    return ind_sum;
}
long int largestValue(int A_size, int* A) {
    // Return the largest value of any of A's nonempty subarrays.
    int i =0;
    int j = 0;
    int sum = 0;
    int m = 0;
    int total_sum = A_size/2;
    int *sum_arr = (int*)malloc(total_sum*sizeof(int));
    int ind_sum = 0;
    int k = 0;
    int max = 0;
    int t = 0;
    //printf("total sum [%d\n]",total_sum);
     for(t=0;t<total_sum;t++){
    sum_arr[t] = first_sum (A,t,A_size);
     }
    /*
    return 0;
    for(t=0;t<total_sum;t++){
    for(i=0;i<A_size;i++){
        for(j=i;j<A_size-i;j++){
            //for(k=j;k<A_size;k++){
                ind_sum = ind_sum + (A[i] * A[j]);    
            //}            
        }
        sum_arr[t] = ind_sum;
        printf("ind_sum [%d]\n",ind_sum);
    }
    }
    */
    max = sum_arr[0];
   // printf("max val[%d]\n",max);
    for(m=1;m<total_sum;m++){
       // printf("max val [%d]\n",sum_arr[m]);
        if(sum_arr[m] > max){
            max = sum_arr[m];
        }
    }
    
    return max;
}

int main() {
    int n; 
    scanf("%i", &n);
    int *A = malloc(sizeof(int) * n);
    for (int A_i = 0; A_i < n; A_i++) {
       scanf("%i",&A[A_i]);
    }
    long int result = largestValue(n, A);
    printf("%ld\n", result);
    return 0;
}