#include <algorithm>
#include <iostream>
#include <queue>
#include <string>
#include <vector>

using namespace std;

static void setup()
{
    cin.tie(0);
    ios::sync_with_stdio(false);
}

struct Action
{
    int pos;
    int point;
};

static void run()
{
    int n;
    cin >> n;

    vector<int> vs;
    vs.resize(n);
    for (auto i = 0; i < n; ++i) {
        cin >> vs[i];
    }

    queue<Action> q;
    q.push(Action{ 0, 0 });
    q.push(Action{ 1, 0 });

    int result = 0;
    while (!q.empty()) {
        const auto action = q.front();
        q.pop();

        if (action.pos >= n) {
            result = max(result, action.point);
            continue;
        }

        q.push(Action{ action.pos + 1, action.point });
        q.push(Action{ action.pos + 2, action.point + vs[action.pos] });
    }

    cout << result << endl;
}

int main(int argc, char **argv)
{
    setup();
    run();
    return 0;
}