#include <fstream>
using namespace std;
ifstream in("oo.in");
ofstream out("oo.out");
int v[100001];
int main()
{
    int i,s=0,n,max1=0;
    in>>n;
    for(i=1; i<=n; i++)
        in>>v[i];
    for(i=1; i<=n-1; i+=3)
        s+=v[i]+v[i+1];
    max1=max(max1,s);
    s=0;
    for(i=2; i<=n-2; i+=3)
        s+=v[i]+v[i+1];
    max1=max(max1,s);
    out<<max1;
    return 0;
}