#include <iostream>
#include <math.h>
using namespace std;

int N;
int V[1000];

int calc(int, int);
int calc_odd(int, int);
int calc_even(int, int);

int calc(int begin, int end)
{
	int num = end - begin + 1;
	if (num <= 0)
	{
		return 0;
	}
	else if (num % 2 == 0)
	{
		return calc_even(begin, end);
	}
	else
	{
		return calc_odd(begin, end);
	}
}

int calc_odd(int begin, int end)
{
	int num = end - begin + 1;
	if (num == 1)
	{
		return V[begin];
	}
	else
	{
		int val1 =
			calc(begin, begin + num / 2 - 1)
			+ calc(begin + num / 2 + 1, end);
		int val2 =
			calc(begin, begin + num / 2 - 2)
			+ V[begin + num / 2]
			+ calc(begin + num / 2 + 2, end);
		return fmax(val1, val2);
	}
}

int calc_even(int begin, int end)
{
	int num = end - begin + 1;

	int val1 =
		calc(begin, begin + num / 2 - 3)
		+ V[begin + num / 2 - 1]
		+ calc(begin + num / 2 + 1, end);
	int val2 =
		calc(begin, begin + num / 2 - 2)
		+ V[begin + num / 2]
		+ calc(begin + num / 2 + 2, end);
	int val3 =
		calc(begin, begin + num / 2 - 2)
		+ calc(begin + num / 2 + 1, end);
	return fmax(fmax(val1, val2),val3);
}

int main() 
{
	cin >> N;
	for (int i = 0; i < N; i++)
	{
		cin >> V[i];
	}

	cout << calc(0, N - 1) << endl;

	return 0;
}