#!/bin/python3

import sys

def largestValue(A):
    # Return the largest value of any of A's nonempty subarrays.
    if len(A) <= 1:
        return A[len(A) - 1]
    sum = 0
    for i in range(len(A)):
        for j in range(i+1,len(A) - 1):
            sum += A[i]*A[j]
           
    return max(sum , largestValue(A[1:]))
if __name__ == "__main__":
    n = int(input().strip())
    A = list(map(int, input().strip().split(' ')))
    result = largestValue(A)
    print(result)