# coding : utf-8
 
import numpy as np
 
N = int(input())

K = [int(i) for i in input().split()]

#DP = [[0 for i in range(N)] for j in range(N)]

def bfs(lt,cost):
	if lt == N:
		return cost + K[lt-1]
	if lt > N:
		return cost
	return max(bfs(lt+1,cost),bfs(lt+2,cost+K[lt-1]))


print(bfs(1,0))