n = int(input())

arr = map(int,raw_input().split())
if n == 1:
	print arr[0]
	quit()
dp = [0 for i in range(n)]
dp[0] = arr[0]
dp[1] = max(arr[0],arr[1])

i = 2
while i < n:
	dp[i] = max(dp[i-2] + arr[i], dp[i-1])

	i += 1

print dp[n-1]