#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

int main() {
	/*
	任意の位置iの皿の合計値の最大

	Take[i] = max(No_Take[i - 1] + v[i],Take[i - 2] + v[i])
	No_Take[i] = max(Take[i - 1],Take[i - 2])
	*/
	int Take[1001] = { 0 };
	int No_Take[1001] = { 0 };
	int num;
	cin >> num;
	vector<int> v;
	for (int i = 0; i < num; i++) {
		int temp; cin >> temp;
		v.push_back(temp);
	}

	if (num == 1) { cout << v[0] << endl; return 0; }

	Take[0] = v[0];Take[1] = v[1];No_Take[0] = 0; No_Take[1] = v[0];

	for (int i = 2; i < num;i++) {
		Take[i] += max(No_Take[i - 1] + v[i], Take[i - 2] + v[i]);
		No_Take[i] += max(Take[i - 1], Take[i - 2]);
	}

	cout << max(Take[num - 1], No_Take[num - 1]) << endl;

	return 0;
}