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

int a [10001];
int mf [10001];

int f (int n) {
    if (n == 0) return 0;
    if (n == 1) return a[1];
    if (mf[n] == INT_MAX)
        mf[n] = a[n] + max (f (n - 1), f (n - 2));
    return mf[n];
}

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