import sys
sys.setrecursionlimit(10000)

n = int(input())
v = list(map(int, input().split()))

memo = {}

def dp(i, f):
	if (i, f) in memo:
		return memo[(i, f)]
	else:
		memo[(i, f)] = dp_inner(i, f)
		return memo[(i, f)]

def dp_inner(i, f):

	if i == 0:
		return v[0] if f else 0
	else:
		
		if f:
			return max(dp(i-1, False) + v[i], dp(i-1, True))
		else:
			return dp(i-1, True)
	
print(max(dp(n-1, True), dp(n-1, False)))