#!/bin/python3

import sys

def largestValue(a):
    # Return the largest value of any of A's nonempty subarrays.
    ans = 0
    for i in range(len(a)-1):
        for j in range(i+1,len(a)):
            tmp_sum = 0
            for x in range(i,j):
                for y in range(x+1,j+1):
                    tmp_sum += a[x]*a[y]
            if tmp_sum > ans:
                ans = tmp_sum
    return ans            
                    
                
            

if __name__ == "__main__":
    n = int(input().strip())
    A = list(map(int, input().strip().split(' ')))
    result = largestValue(A)
    print(result)