#include <fstream>
#include <vector>
#include <algorithm>

using namespace std;

ifstream in("oo.in");
ofstream out("oo.out");

int main()
{
    int n, maxim;
    in >> n;

    vector<int> v(n + 1);
    vector<vector<int> > dp1(n + 1, vector<int>(2));
    vector<vector<int> > dp2(n + 1, vector<int>(2));
    vector<vector<int> > dp3(n + 1, vector<int>(2));

    for (int i = 1; i <= n; i++)
        in >> v[i];

    dp1[2][1] = maxim = v[1] + v[2];
    for (int i = 3; i < n; i++)
    {
        dp1[i][0] = max(dp1[i - 1][0], dp1[i - 1][1]);
        dp1[i][1] = dp1[i - 2][0] + v[i - 1] + v[i];
        maxim = max(maxim, max(dp1[i][0], dp1[i][1]));
    }

    dp2[n - 1][1] = v[n - 1] + v[n];
    for (int i = n - 2; i > 1; i--)
    {
        dp2[i][0] = max(dp2[i + 1][0], dp2[i + 1][1]);
        dp2[i][1] = dp2[i + 2][0] + v[i + 1] + v[i];
        maxim = max(maxim, max(dp2[i][0], dp2[i][1]));
    }

    for (int i = 4; i <= n - 2; i++)
    {
        dp3[i][0] = max(dp3[i - 1][0], dp3[i - 1][1]);
        dp3[i][1] = dp3[i - 2][0] + v[i - 1] + v[i];
        maxim = max(maxim, max(dp3[i][0], dp3[i][1]));
    }

    out << maxim;
    return 0;
}