#include <fstream>
#include <algorithm>

using namespace std;

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

int main()
{
    long int n,s1=0,s2=0;
    f>>n;
    long int v[n+1],b[n+1];
    for(int i=1;i<=n;i++)
    {
        f>>v[i];
        b[i-1]=v[i];
    }
    for(int i=1;i<=n;i++)
    {
        if(v[i]!=0)
        {
            s1=s1+v[i]+v[i+1];
            if(i-1==0)
                v[n]=0;
            v[i-1]=0;v[i]=0;v[i+1]=0;v[i+2]=0;
        }
        if(b[i]!=0)
        {
            s2=s2+b[i]+b[i+1];
            b[i-1]=0;b[i]=0;b[i+1]=0;b[i+2]=0;
        }
    }
    if(s1>s2)
        g<<s1;
    else
        g<<s2;
    return 0;
}