#include <fstream>
#include <cmath>
using namespace std;

ifstream f("oo.in");
ofstream g("oo.out");

int n, a[100003], dp1[100003], dp2[100003], dp3[100003];
int main()
{
	int i;
	f >> n;
	for (i = 1; i <= n; i++)
		f >> a[i];
	dp1[2] = dp1[3] = a[1] + a[2];
	dp2[3] = a[2] + a[3];
	dp3[1] = a[n] + a[1];
	for (i = 4; i <= n; i++)
	{
		if (i < n - 1) dp3[i] = max(dp3[i - 1], dp3[i - 3] + a[i] + a[i - 1]);
		if (i < n) dp1[i] = max(dp1[i - 1], dp1[i - 3] + a[i] + a[i - 1]);
		dp2[i] = max(dp2[i - 1], dp2[i - 3] + a[i] + a[i - 1]);
	}
	g << max( dp2[n], max(dp1[n - 1], dp3[n - 2] )) << "\n";
}