#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 + 1, 0);
    dp[0] = INT_MAX;

    dp[1] = v[0];

    for (int i = 2; i <= n; i++) {
        if (i - 1 >= 1) {
            dp[i] = dp[i - 1];
        } if (i - 3 >= 1) {
            dp[i] = max(dp[i], dp[i - 3]);
        } if (i - 5 >= 1) {
            dp[i] = max(dp[i], dp[i - 5]);
        }

        dp[i] += v[i - 1];
    }

    cout << dp[n] << endl;

    executeTime();
    return 0;
}