#!/bin/python

from itertools import combinations
import sys

def subA(A):
    for i in xrange(len(A)-1):
        for j in xrange(i, len(A)):
            yield A[i:j]
            
def product(A):
    return sum(a*b for a,b in combinations(A, 2))

def largestValue(A):
    # Return the largest value of any of A's nonempty subarrays.
    return max(product(x) for x in subA(A))

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