#include <iostream>
using namespace std;

#define N 1000

int n;
int v[N];
int mx[N];

int dfs(int i)
{
	if ( i >= n - 2 ) {
		return v[i];
	}

	int max = 0;
	for ( int j = i + 2; j < n; j++ ) {
		max = max < mx[j] ? mx[j] : max;
	}

	return v[i] + max;
}

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

	int max = 0;
	for ( int i = n; i--; ) {
		mx[i] = dfs(i);
		max = max < mx[i] ? mx[i] : max;
	}

	cout << max;

	return 0;
}