enter_num = int(input())
lst = list(map(int,input().split()))
lst1 = []
for i in range(enter_num):
k = 1
j = 1
while j+k < len(lst):
k += 1
k = k*k
j = k - j
k = k**(0.5)
sum = sum(lst[ : int(j)])
lst = lst[1 : ]
lst1.append(sum)
del sum
print(max(lst1))
what is time complexity without using sum method