#include <stdio.h>
#include <stdlib.h>
 
long long int maxSubArraySum(long long int a[],long long int size,long long int *begin,long long int *end)
{
    long long int max_so_far = 0, max_end = 0;
    long long int i, current_index = 0;
 
    for (i = 0; i < size; i++)
    {
        max_end = max_end + a[i];
        if (max_end <= 0)
        {
            max_end = 0;
            current_index = i + 1;
        }
        else if (max_so_far < max_end)
        {
            max_so_far = max_end;
            *begin = current_index;
            *end = i;
        }
   }
   return max_so_far;
}
 
int main()
{
    long long int n,sum=0,i,j,b,c;
    scanf("%lld",&n);
    long long int arr[n];
    for(i=0;i<n;i++)
        scanf("%lld",&arr[i]);
    long long int start = 0, end = 0;
    long long int size = sizeof(arr) / sizeof(arr[0]);
 printf(" The begin and End are %lld & %lld", start, end);
   b=start;
    c=end;
    for(i=b;i<c;i++)
    {
        for(j=i+1;j<=c;j++)
        {
            sum=sum+(arr[i]*arr[j]);
        }
    }
    printf("%lld\n",sum);
    getchar();
    return 0;
}