/*
 * main.cpp
 *
 *  Created on: 2017/10/06
 *      Author: sep
 */

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <string>
#include <cmath>
#include <cstring>
#include <vector>
#include <algorithm>
#include <map>
#include <queue>

using namespace std;

inline int main003();
inline int main045();
inline int main3();
inline int main4();

#define TEST

int main() {

#ifdef TEST
	while (1)
#endif
		main045();

	return 0;
}

inline int get_bit(int x) {

	int c = 0;

	while (x) {
		if (x & 1)
			c++;
		x >>= 1;
	}
	return c;
}

inline int main003() {

	int num;
	int route, v1, v2, bit_count;
	int result = 0;
	map<int, int> v;
	queue<int> q;

	cin >> num;

	q.push(1);

	v[1] = 1;

	while (!q.empty()) {

		route = q.front();
		q.pop();

		if (route == num) {
			result = v[route];
			break;
		}

		bit_count = get_bit(route);

		v1 = route + bit_count;
		v2 = route - bit_count;

		if ((v1 <= num) && (v[v1] == 0 || v[route] + 1 < v[v1])) {
			v[v1] = v[route] + 1;
			q.push(v1);
		}

		if ((0 < v2) && (v[v2] == 0 || v[route] + 1 < v[v2])) {
			v[v2] = v[route] + 1;
			q.push(v2);
		}

	}

	if (result == 0) {
		cout << -1;
	} else {
		cout << result;
	}

	return 0;

}

inline int main045() {

	int num;
	int *value;
	int **c_value;
	int i;

	cin >> num;

	value = new int[num];
	c_value = new int*[num];

	for (i = 0; i < num; i++) {
		cin >> value[i];
		c_value[i] = new int[2];

	}

	c_value[0][0] = 0;
	c_value[0][1] = value[0];

	if (num > 1) {
		c_value[1][0] = value[0];
		c_value[1][1] = value[1];
	}

	for (i = 2; i < num; i++) {
		c_value[i][0] = max(c_value[i - 1][1], c_value[i - 2][1]);
		c_value[i][1] = max(c_value[i - 1][0] + value[i],
				c_value[i - 2][0] + value[i]);
	}

	cout << max(c_value[num - 1][0], c_value[num - 1][1]);

	return 0;
}