#include<iostream>
#include <stdio.h>
#include <string>
#include <string.h>
#include <algorithm>
#include <functional>
#include <vector>

using namespace std;
int main()
{
	int N = 0;
	int V[1024];

	cin >> N;
	for (int i = 1; i < N + 1; i++) {
		cin >> V[i];
	}

	int dp[1024];

	dp[1] = V[1];
	dp[2] = max(V[1], V[2]);

	for (int i = 3; i < N + 1; i++) {
		dp[i] = max(dp[i - 1], dp[i - 2] + V[i]);
	}

	cout << dp[N];

	return 0;
}