import sys

def check(a,b,x):
	if x < a or x > b:
		sys.exit()

def cal_choice(list,N):

	cal = []
	for i in range(0,N):
		cal.append(0)

	cal[N-1] = list[N-1]
	cal[N-2] = max(list[N-1],list[N-2])

	i = N - 3

	while i >= 0:
		cal[i] = max(list[i]+cal[i+2],cal[i+1])
		i -= 1
	return cal



N = int(input())
check(1,1000,N)

list = input().split(' ')

for i in range(0,len(list)):
	list[i] = int(list[i])
	check(1,100,list[i])

print(cal_choice(list,N)[i])