#include<iostream>
using namespace std;

int main() {

	int num;
	cin >> num;

	int *list = new int[num];
	int *max = new int[num];
	for (int i = 0; i < num; i++) {
		cin >> list[i];
		max[i] = 0;
	}

	if (num == 1) {
		max[0] = list[0];
	}
	else if (num == 2) {
		max[1] = list[0] + list[1];
	}
	else {
		max[0] = list[0];
		max[1] = list[0] + list[1];
		for (int i = 2; i < num; i++) {
			max[i] = max[i - 1];
			if (max[i] < list[i] + list[i - 1] + max[i - 3]) {
				max[i] = list[i] + list[i - 1] + max[i - 3];
			}
			if (max[i] < max[i - 2] + list[i]) {
				max[i] = max[i - 2] + list[i];
			}
		}
	}

	cout << max[num - 1] << endl;

	delete[] max;
	delete[] list;
	return 0;
}