from collections import deque

N = int(input())
sushi = [ int(i) for i in input().split() ]
sushi.insert(0,0)

res = [0] * (N + 1)
q = deque([])

res[0] = 0
q.append(0)
taboo = False

while q:
    pos = q.popleft()
    
    for next_pos in range(pos+1,N+1):
        if taboo:
            if next_pos == pos + 1:
                continue
        if res[next_pos] < res[pos] + sushi[next_pos]:
            q.append(next_pos)
            res[next_pos] = res[pos] + sushi[next_pos]

    taboo = True
    
print(max(res))