#include <vector>
#include <fstream>
#include <algorithm>
#define NMax 100002
using namespace std;
vector <int> vect;int aux[NMax];
int main()
{
    ifstream in("oo.in");
    ofstream out("oo.out");
    int i, n,maxim=0;
    in >> n;
    vect.push_back(0)
    for (i = 1;i <= n;i++)
    {
        in >> k;
        vect.push_back(k);
    }
    vect.push_back(0)
    vect[0] = vect[n];
    vect[n + 1] = vect[1];
    aux[0] = vect[0] + vect[1];
    aux[1] = vect[1] + vect[2];
    aux[2] = vect[2] + vect[3];
    for (i = 3;i < n - 2;i++)
    {
        aux[i] = max(vect[i] + vect[i + 1] + aux[i - 3], aux[i - 1]);
    }
    maxim = aux[n - 3];
    aux[0] = 0;
    aux[1] = vect[1] + vect[2];
    aux[2] = vect[2] + vect[3];
    for (i = 3;i < n-1;i++)
    {
        aux[i] = max(vect[i] + vect[i + 1] + aux[i - 3], aux[i - 1]);
    }
    maxim = max(maxim, aux[n - 2]);
    aux[0] = 0;
    aux[1] = 0;
    aux[2] = vect[2] + vect[3];
    for (i = 3;i < n;i++)
    {
        aux[i] = max(vect[i] + vect[i + 1] + aux[i - 3], aux[i - 1]);
    }
    maxim = max(maxim, aux[n-1]);
    out << maxim;
}