#!/bin/python3

import sys

def largestValue(A):
    n=len(A)
    mx=0
    for i in range(n):
        for j in range(i+1,n):
            b=A[i:j+1]
            lb=j-i+1
            res=sum([b[ii]*b[jj] for ii in range(lb) for jj in range(lb) if ii!=jj])//2
            mx=max(mx,res)
    return mx
            

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