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

int a [10001];
int f [10001];

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