#include <fstream>
#define mF "oo"
std::ifstream in(mF ".in");
std::ofstream out(mF ".out");
constexpr int N = 100000; int V[N], X[N], n;
int Q(int i, int j)
{
    for (; i < j; i++) X[i] = std::max(X[i-1], X[i-3] + V[i-1] + V[i]);
    return X[i-1];
}
int R(int i)
{
    for (int p = i; p--;) X[p] = 0;
    return std::max(Q(i, n), Q(i, n-5+i) + (i>2? V[i-2]: V[n-3+i]) + (i>3? V[i-3]: V[n-4+i]));
}
int main()
{
    int r = 0; in >> n; for (int i = 0; i < n; i++) in >> V[i];
    for (int i = 2; i <= 4; i++) r = std::max(r, R(i));
    out << r;
}