#include <iostream>
#include <fstream>

using namespace std;

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

const int NMAX = 100000 + 5;

int n;
int v[NMAX], dp[NMAX];

void Read()
{
    fin >> n;
    for (int i = 1; i <= n; ++i)
        fin >> v[i];
}

int main()
{
    Read();
    dp[n] = v[n] + v[1];
    for (int i = n - 1; i >= 1; --i)
    {
        dp[i] = v[i] + v[i + 1] + dp[i + 3];
        if (dp[i + 3] > dp[i])
            dp[i] = dp[i + 3];
    }
    fout << dp[1];
}