#include <iostream>
#include <vector>
using namespace std;

int main() {
    int n, even = 0, odd = 0;
    cin >> n;
    vector<int> v(n);
    for(int i=0;i<n;i++) cin >> v[i];

    vector<int> ans(n, 0);
    for(int i=0;i<n;i++) {
        if(i-3>=0)
            ans[i] = max(ans[i-2], ans[i-3]) + v[i];
        else if(i-2>=0)
            ans[i] = ans[i-2] + v[i];
        else
            ans[i] = v[i];
    }

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

}