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

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

    arr_sum[1] = arr[1];
    arr_sum[2] = arr[1] + arr[2];
    arr_sum[3] = max(arr[1] + arr[3], arr[2] + arr[3]);

    for (int i = 4;i <= n;i++) {
        arr_sum[i] = max(arr_sum[i-3] + arr[i-1] + arr[i],arr_sum[i-2]+arr[i]);
    }

    cout << arr_sum[n];
    return 0;
}