def max_subarray(A):
    ar=[]
    max_ending_here = max_so_far = A[0]
    for x in A[1:]:
        max_ending_here = max(x, max_ending_here + x)
        max_so_far = max(max_so_far, max_ending_here)
        ar.append(x)
    return ar


n = int(raw_input().strip())
A = map(int, raw_input().strip().split(' '))

a=max_subarray(A)
x=sum(a[:n-2])**2

c=0
for i in range(len(a)-1):
    c+=a[i]**2 
print (x-c)/2