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

int CalcMaxValue(int n, int index, int* values, int* memo) {

	if (index >= n)
		return 0;

	if (memo[index] == 0) {
		memo[index] = max(
			values[index] + CalcMaxValue(n, index + 2, values, memo),
			CalcMaxValue(n, index + 1, values, memo));
	}

	return memo[index];
}

int main() {
	int n;
	cin >> n;
	
	int memo[1000];
	int values[1000];

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

	cout << CalcMaxValue(n, 0, values, memo) << endl;

	return 0;
}