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

void executeTime() {
    cerr << "Time Taken: " << (float)clock() / CLOCKS_PER_SEC << " secs";
}

int main() {


    int n;
    cin >> n;

    vector<int> v(n);
    for (auto &x : v)
        cin >> x;

    vector<int> dp(n, 0);

    dp[0] = max(v[0], 0);

    if (n >= 2)
        dp[1] = max({v[0], v[1], 0});

    for (int i = 2; i < n; i++) {
        dp[i] = max(dp[i - 1], dp[i - 2] + v[i]);
    }

    cout << dp[n - 1] << endl;

    executeTime();
    return 0;
}