def dfs(N,V,i):
	if i >= N:return 0
	ret = 0
	ret = max(ret,dfs(N,V,i + 2) + V[i])
	ret = max(ret,dfs(N,V,i + 3) + V[i])
	return ret

N = int(raw_input())
V = map(int,raw_input().split())
print max(dfs(N,V,0),dfs(N,V,1))