#include <fstream>

using namespace std;
int v[100001],profit[100001];
int main()
{
    ifstream fin("oo.in");
    ofstream fout("oo.out");
    int n,i,j;
    fin>>n;
    for (i=1;i<=n;i++)
    {
        fin>>v[i];
    }
    profit[2]=v[1]+v[2];
    for (i=3;i<=n;i++)
    {
        if (i-3>0)
        profit[i]=max(profit[i-1],v[i-1]+v[i]+profit[i-3]);
        else
        profit[i]=max(profit[i-1],v[i-1]+v[i]);
    }
        fout<<profit[n-1]<<" ";
    return 0;
}