n=int(input())
a=list(map(int,input().split()))
max=0
for i in range(n):
    j=i
    sum=0
    k=j+1
    while k<n:
        for l in range(i,j+1):
            sum+=(a[l]*a[k])
        if sum>max:
            max=sum
        k+=1
        j+=1
print(max)