#include<fstream>
using namespace std;
int v[100003],i,n,D[100003],x;
int maxim(int x,int y)
    {
        if(x>y) return x;
        else return y;
}

int main()
{
    ifstream f("oo.in");
    ofstream g("oo.out");
    f>>n;
    for(i=1;i<=n;i++)
        f>>v[i];
    D[1]=0;
    D[2]=0;
    D[3]=v[2]+v[3];
    for(i=4;i<=n;i++)
        D[i]=maxim(D[i-1],v[i]+v[i-1]+D[i-3]);
    x=D[n];
    D[1]=0;
    D[2]=v[1]+v[2];
    D[3]=v[1]+v[2];
    for(i=4;i<=n-1;i++)
        D[i]=maxim(D[i-1],v[i]+v[i-1]+D[i-3]);
    x=maxim(x,D[n-1]);
    v[n+1]=v[1];
    for(i=2;i<=n+1;i++)
        v[i-1]=v[i];
    D[1]=0;
    D[2]=0;
    D[3]=v[2]+v[3];
    for(i=4;i<=n;i++)
        D[i]=maxim(D[i-1],v[i]+v[i-1]+D[i-3]);
    x=maxim(x,D[n]);
    g<<x;
    return 0;
}