#include<fstream>
using namespace std;
const int dim=1e5+2;
int v[dim],S[dim];
ifstream f("oo.in");
ofstream g("oo.out");
int main()
{
    int i,j,n,mx=0;

    f>>n;
    for(i=1;i<=n;i++)
    {
        f>>v[i];
    }

    //caz I - luam sectoarele 1 si 2
    S[2]=S[3]=S[4]=v[1]+v[2];
    for(i=5;i<n;i++)
    {
        S[i]=max(S[i-1],v[i-1]+v[i]+S[i-3]);
    }
    mx=S[n-1];

    //caz II - luam sectoarele 1 si n
    S[1]=S[2]=S[3]=v[1]+v[n];
    for(i=4;i<n-1;i++)
    {
        S[i]=max(S[i-1],v[i-1]+v[i]+S[i-3]);
    }
    mx=max(mx,S[n-2]);

    //caz III - nu luam sectorul 1
    S[1]=S[2]=0;
    for(i=3;i<=n;i++)
    {
        S[i]=max(S[i-1],v[i-1]+v[i]+S[i-3]);
    }
    mx=max(mx,S[n]);
    g<<mx;

    return 0;
}