// https://yukicoder.me/problems/no/45
#include <bits/stdc++.h>
using namespace std;

int dp[1005];
int main() {
    int n;
    cin >> n;
    vector<int> v(n);
    for (int i = 0; i < n; i++) {
        cin >> v[i];
    }
    for (int i = 0; i < n; i++) {
        dp[i + 2] = max(dp[i + 2], dp[i] + v[i]);
        dp[i + 3] = max(dp[i + 3], dp[i] + v[i]);
    }
    cout << max({dp[n], dp[n + 1], dp[n + 2]}) << endl;

    return 0;
}