#include <fstream>

using namespace std;
ifstream fin ("oo.in");
ofstream fout("oo.out");

int D[100010], v[100010];
int n, sol, i;
int main () {

    fin>>n;
    for (i=1;i<=n;i++)
        fin>>v[i];
    D[1] = 0;
    D[2] = v[1] + v[2];
    D[3] = 0;
    for (i=4; i<n; i++)
        D[i] = max(D[i-1], v[i] + v[i-1] + D[i-3]);
    sol = D[n-1];

    D[1] = 0;
    D[2] = 0;
    D[3] = v[2] + v[3];
    for (i=4; i<=n; i++)
        D[i] = max(D[i-1], v[i] + v[i-1] + D[i-3]);
    sol = max(sol, D[n]);

    D[1] = 0;
    D[2] = 0;
    D[3] = 0;
    for (i=4; i<n-1; i++)
        D[i] = max(D[i-1], v[i] + v[i-1] + D[i-3]);

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

    fout<<sol;

    return 0;
}