#include <fstream>
using namespace std;
ifstream fin("oo.in");
ofstream fout("oo.out");
const int MAXN = 100005;
int n;
int v[MAXN];
int s[MAXN];
int sol;
int main() {
    fin >> n;
    for (int i = 1; i <= n; ++i) {
        fin >> v[i];
    }
    s[2] = s[3] = s[4] = v[1] + v[2];
    for (int i = 5; i < n; ++i) {
        s[i] = max(s[i - 1], v[i] + v[i - 1] + s[i - 3]);
    }
    sol = s[n - 1];
    s[1] = s[2] = s[3] = v[n] + v[1];
    for (int i = 4; i <= n; ++i) {
        s[i] = max(s[i - 1], v[i] + v[i - 1] + s[i - 3]);
    }
    sol = max(sol, s[n - 2]);
    s[0] = s[1] = s[2] = 0;
    for (int i = 3; i <= n; ++i) {
        s[i] = max(s[i - 1], v[i] + v[i - 1] + s[i - 3]);
    }
    sol = max(sol, s[n]);
    fout << sol;
    fout.close();
    return 0;
}