#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<int> dp(n + 1);

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

    dp[2] = dp[3] = dp[4] = v[1] + v[2];
    for (int i = 5; i < n; i++)
    {
        dp[i] = max(dp[i - 1], dp[i - 3] + v[i - 1] + v[i]);
        maxim = max(maxim, dp[i]);
    }

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

    dp[1] = dp[2] = dp[3] = v[1] + v[n];
    for (int i = 4; i <= n - 2; i++)
    {
        dp[i] = max(dp[i - 1], dp[i - 3] + v[i - 1] + v[i]);
        maxim = max(maxim, dp[i]);
    }

    out << maxim;
    return 0;
}