#include <iostream>
#include <algorithm>
using namespace std;

int n;
int memo[1000];
int values[1000];

int CalcMaxValue(int index) {

	if (index >= n)
		return 0;

	if (memo[index] != -1)
		return memo[index];

	int ret = max(
		values[index] + CalcMaxValue(index + 2),
		CalcMaxValue(index + 1));

	memo[index] = ret;

	return ret;
}

int main() {
	cin >> n;
	for (int i = 0; i < n; i++) {
		cin >> values[i];
		memo[i] = -1;
	}

	cout << CalcMaxValue(0) << endl;

	return 0;
}