#include <fstream>

using namespace std;

int N;
int v[100010];
int dp[100010][3];

void Citire () {
	ifstream fin ("oo.in");
	fin >> N;
	for (int i = 1; i <= N; i++)
		fin >> v[i];
	fin.close ();
}

int Business () {
	dp[1][1] = v[1] + v[N];
	dp[2][1] = dp[1][1];
	dp[2][2] = v[1] + v[2];
	dp[3][0] = v[3] + v[2];
	dp[3][1] = dp[2][1];
	dp[3][2] = dp[2][2];
	dp[4][0] = max (dp[3][0], v[4] + v[3]);
	dp[4][1] = max (v[4] + v[3] + dp[1][1], dp[3][1]);
	dp[4][2] = dp[2][2];
	dp[5][0] = max (v[5] + v[4], dp[4][0]);
	dp[5][1] = max (v[5] + v[4] + dp[2][1], dp[4][1]);
	dp[5][2] = dp[4][2] + v[5] + v[4];
	if (N <= 6) dp[1003123][312] = 1;
	for (int i = 6; i < N - 1; i++)
	{
		dp[i][0] = max (v[i] + v[i - 1] + dp[i - 3][0], dp[i - 1][0]);
		dp[i][1] = max (v[i] + v[i - 1] + dp[i - 3][1], dp[i - 1][1]);
		dp[i][2] = max (v[i] + v[i - 1] + dp[i - 3][2], dp[i - 1][2]);
	}
	dp[N - 1][0] = max (v[N - 1] + v[N - 2] + dp[N - 4][0], dp[N - 2][0]);
	dp[N - 1][1] = dp[N - 2][1];
	dp[N - 1][2] = max (v[N - 1] + v[N - 2] + dp[N - 4][0], dp[N - 2][0]);
	dp[N][0] = max (v[N] + v[N - 1] + dp[N - 3][0], dp[N - 1][0]);
	dp[N][1] = dp[N - 1][1];
	dp[N][2] = dp[N - 1][2];
	return max (dp[N][0], max (dp[N][1], dp[N][2]));
}

void Scriere () {
	ofstream fout ("oo.out");
	fout << Business ();
	fout.close ();
}

int main () {
	Citire ();
	Scriere ();
	return 0;
}