#include <iostream>
using namespace std;

const int kMAX_N = 1010;

int N;
int V[kMAX_N];
int max_taste[kMAX_N];

void Solve() {
    for (int i = 0; i < N; i++) {
        max_taste[i + 1] = max(max_taste[i + 1], max_taste[i]);
        max_taste[min(N, i + 2)] = max(max_taste[min(N, i + 2)],
                                       max_taste[i] + V[i]);
    }
    cout << max_taste[N] << endl;
}

int main() {
    cin >> N;

    for (int i = 0; i < N; i++) {
        cin >> V[i];
    }

    Solve();
    return 0;
}