#include <fstream>
#define DIM 100002

using namespace std;

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

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

int main()
{
    f>>n;
    for(int i = 1; i <= n; ++ i)
        f>>v[i];

    //1//////////////////////////////
    dp[1] = 0;
    dp[n] = 0;
    dp[2] = v[1] + v[2];
    dp[3] = dp[2];
    for(int i = 4; i <= n - 1; ++ i){
        dp[i] = max(dp[i - 1], max(dp[i - 2], max(dp[i - 3] + v[i - 1] + v[i], dp[i - 4] + v[i - 1] + v[i])));
    }
    g<<max(dp[n - 1], max(dp[n - 2], max(dp[n - 3], dp[n - 4])));

    return 0;
}