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

int a [10001];


int f (int n) {
    if (n == 0) return 0;
    if (n == 1) return a[1];

    return a[n] + max (f (n - 1), f (n - 2));
}


int main () {
    int n;  cin >> n;
    for (int i = 1; i <= n; i++)  cin >> a[i];

    cout << f (n) << endl;
    return 0;
}