#include<fstream>
using namespace std;
ifstream f("oo.in");
ofstream g("oo.out");
int n,v[100001],nr=0;
int main()
{
    int i;
    f>>n;
    for(i=1;i<=n;i++)
        f>>v[i];
    v[0]=v[n];
    v[n+1]=v[1];
    v[n+2]=v[2];
    for(i=1;i<=n;i++)
    {
        if(v[i]+v[i+1]>v[i-1]+v[i+2] && v[i]!=0 && v[i+1]!=0)
        {
            nr=nr+v[i]+v[i+1];
            v[i]=v[i+1]=v[i-1]=v[i+2]=0;
            i+=3;
        }

    }
    g<<nr;
    f.close();
    g.close();
    return 0;
}