def dfs(i,n):
	global N
	global V
	global dp
	if i >= N:return 0
	if dp[n][i] != -1:return dp[n][i]
	ret = 0
	ret = max(ret,dfs(i + 2,n) + V[i])
	ret = max(ret,dfs(i + 3,n) + V[i])
	dp[n][i] = ret
	return dp[n][i]
N = int(raw_input())
V = map(int,raw_input().split())
dp = [[-1 for j in range(N)] for i in range(2)]
print max(dfs(0,0),dfs(1,1))