#!/bin/python

import sys
def value(A):
    n=len(A)
    ans=0
    for i in range(n):
        for j in range(i+1,n):
            ans+=A[i]*A[j]
    return ans
            
def largestValue(A):
    # Return the largest value of any of A's nonempty subarrays.
    n=len(A)
    vmax=A[0]
    for i in range(n):
        for j in range(i+1,n):
            v=value(A[i:j+1])
            #print (i,j,v)
            if v > vmax:
                vmax=v
    return vmax
    

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