#include <fstream>

using namespace std;

ifstream cin("oo.in");
ofstream cout("oo.out");

const int NMAX = 1e5;

int n;
int a[NMAX + 1];
int dp[NMAX + 1][2];
int ans;

void Reset()
{
	for (int i = 1; i <= n; i++)
		dp[i][0] = dp[i][1] = 0;
}

int main()
{
	cin >> n;
	for (int i = 1; i <= n; i++)
		cin >> a[i];

	
	// [1, n - 1]
	for (int i = 2; i <= n - 1; i++)
	{
		dp[i][0] = max(dp[i - 1][1], dp[i - 1][0]);
		dp[i][1] = dp[i - 2][0] + a[i] + a[i - 1];
	}

	ans = max(dp[n][0], dp[n][1]);

	Reset();

	// [2, n]
	for (int i = 3; i <= n; i++)
	{
		dp[i][0] = max(dp[i - 1][1], dp[i - 1][0]);
		dp[i][1] = dp[i - 2][0] + a[i] + a[i - 1];
	}

	ans = max(ans, max(dp[n][0], dp[n][1]));

	Reset();

	// [3, n - 2]
	for (int i = 4; i <= n - 2; i++)
	{
		dp[i][0] = max(dp[i - 1][1], dp[i - 1][0]);
		dp[i][1] = dp[i - 2][0] + a[i] + a[i - 1];
	}

	ans = max(ans, max(dp[n][0], dp[n][1]));

	cout << ans;


	return 0;
}