#include <fstream>

using namespace std;

int v[100010];
int D[100010];
int n, sol, i;

int main () {


    ifstream f ("oo.in");
    ofstream g("oo.out");
    f>>n;
    for (i=1;i<=n;i++)
    {
        f>>v[i];
    }
    D[1] = 0;
    D[2] = 0;
    D[3] = v[2]+v[3];
    for (i=4;i<=n;i++)
        D[i] = max(D[i-1], D[i-3] + v[i]+v[i-1]);
    sol = D[n];
    D[1] = 0;
    D[2] = v[1]+v[2];
    D[3] = max(v[2]+v[3], v[1]+v[2]);
    for (i=4;i<n;i++)
        D[i] = max(D[i-1], D[i-3] + v[i]+v[i-1]);
    sol = max(sol, D[n-1]);
    D[2] = 0;
    D[3] = 0;
    D[4] = v[3]+v[4];
    for (i=5;i<=n-2;i++)
        D[i] = max(D[i-1], D[i-3] + v[i]+v[i-1]);

    sol = max(sol, D[n-2] + v[1] + v[n]);

    g<<sol;
    return 0;
}






///In caz ca se uita cineva: da e inspirata problema, dar am inteles-o       :))))))