/*
 * 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();

int main() {

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

	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];
	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;
}