#include <iostream>
#include <string>
#include <sstream>
#include <vector>
using namespace std;

int sushiSumMaxValue(vector<int> sushiValues) {
	int sushiCount = (int)sushiValues.size();

	vector<int> sushiSumValues;
	sushiSumValues.push_back(sushiCount > 0 ? sushiValues[0] : 0);
	sushiSumValues.push_back(sushiCount > 1 ? sushiValues[1] : 0);
	sushiSumValues.push_back(sushiSumValues[0] + (sushiCount > 2 ? sushiValues[2] : 0));

	for (int i = 3; i < sushiCount; ++i) {
		sushiSumValues.push_back(sushiValues[i]
			+ (sushiSumValues[i - 2] > sushiSumValues[i - 3] ? sushiSumValues[i - 2] : sushiSumValues[i - 3]));
	}

	int sushiSumCount = (int)sushiSumValues.size();
	return sushiSumValues[sushiSumCount - 1] > sushiSumValues[sushiSumCount - 2]
		? sushiSumValues[sushiSumCount - 1] : sushiSumValues[sushiSumCount - 2];
}

int main() {
	vector<int> sushiValues;

	string tmp;
	cin >> tmp;

	while (cin >> tmp) {
		sushiValues.push_back(stoi(tmp));
	}

	cout << sushiSumMaxValue(sushiValues) << endl;
}