#include <bits/stdc++.h>
using namespace std;

int main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);

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