N = int(input())
lst = list(int(input()) for _ in range(N))
dp = [0 for _ in range(N)]
for i in range(N):
if i == 0:
dp[0] = lst[0]
elif i == 1:
dp[1] = max(lst[0] + lst[1], lst[0], lst[1])
else:
dp[i] = max(dp[i-2] + lst[i], dp[i-3] + lst[i-1] + lst[i])
print(dp[-1])