D

#define _CRT_SECURE_NO_DEPRECATE

#include <iostream>
#include <vector>
#include <string>
#include <map>
#include <set>
#include <algorithm>

#define ull unsigned long long
#define ll long long

using namespace std;

ll d[101];
ll a[101];

int main() {
	//freopen("input.txt", "r", stdin);
	//freopen("output.txt", "w", stdout);
	int n;
	cin >> n;

	for (int i = 1; i <= n; i++) {
		cin >> a[i];
		d[i] = 0;
	}
	d[0] = 0;
	d[1] = a[1];
	for (int i = 2; i <= n; i++) {
		d[i] = a[i] + max(d[i - 1], d[i - 2]);
	}
	cout << d[n];
	return 0;
}