//https://www.infoarena.ro/problema/oo
#include <fstream>
#include <vector>

std::ifstream fin("oo.in");
std::ofstream fout("oo.out");

using namespace std;

vector<int> dp, v;

int max(int a, int b)
{
	return a > b ? a : b;
}
int main()
{
	int n, maxim = 0;
	fin >> n;
	v.resize(n + 1);
	dp.resize(n + 1, 0);
	for (int i = 1; i <= n; ++i)
		fin >> v[i];


	dp[1] = v[1] + v[n];
	for (int i = 3; i < n; ++i)
		dp[i] = max(dp[i - 1], dp[i - 3] + v[i] + v[i - 1]);
	maxim = max(maxim, dp[n - 2]);

	//for (int i = 0; i <= n; ++i)
	//	fout << dp[i] << ' ';
	//fout << '\n';
	dp.clear();
	dp.resize(n + 1, 0);
	dp[3] = v[3] + v[2];
	for (int i = 4; i <= n; ++i)
		dp[i] = max(dp[i - 1], dp[i - 3] + v[i] + v[i - 1]);
	dp[0] = max(dp[n], v[n] + v[n - 1] + dp[n - 3]);
	maxim = max(maxim, dp[0]);

	/*for (int i = 0; i <= n; ++i)
		fout << dp[i] << ' ';
	fout << '\n';*/

	dp.clear();
	dp.resize(n + 1, 0);
	dp[2] = v[1] + v[2];
	for (int i = 3; i < n; ++i)
		dp[i] = max(dp[i - 1], dp[i - 3] + v[i] + v[i - 1]);
	maxim = max(maxim, dp[n - 1]);

	//for (int i = 0; i <= n; ++i)
	//	fout << dp[i] << ' ';
	//fout << '\n';

	fout << maxim << '\n';
}