def max(x,y):
	if x >= y:
		return x
	else:
		return y

n = int(input())
v = list(map(int,input().split()))
table = [0 for i in range(n)]
for i in range(n):
	if i == 0:
		table[0] = v[0]
	elif i == 1:
		table[1] = max(v[0],v[1])
	else:
		table[i] = max(table[i-2]+v[i],table[i-1])
print(table[n-1])