#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("oo.in");
ofstream fout("oo.out");
int n,a[100010],d[100010],rez,k;
int main()
{
    fin>>n;
    for(int i=1;i<=n+5;i++)
        fin>>a[i+5];
    for(int i=n+1;i<=n+5;i++)
    {
        k++;
        d[k]=a[i];
    }
    for(int i=6;i<=n+5;i++)
    {
        d[i]=a[i]+a[i-1]+max(d[i-3],max(d[i-4],d[i-5]));
        if(rez<d[i])
            rez=d[i];
    }
    fout<<rez;
    return 0;
}