#include <fstream>
using namespace std;
ifstream cin("oo.in");
ofstream cout("oo.out");
int n, m, i, j, aux, d[100005], v[100005];
int main () {
    cin>>n;
    for (i=1;i<=n;i++){
        cin>>v[i];
    }
    d[3]=v[2]+v[3];
    for (i=4;i<=n;i++)
        d[i]=max(d[i-1],d[i-3]+v[i-1]+v[i]);
    aux=d[n];
    d[2]=v[1]+v[2];
    d[3]=max(v[2]+v[3],v[1]+v[2]);
    for (i=4;i<=n-1;i++)
        d[i]=max(d[i-1],d[i-3]+v[i-1]+v[i]);
    aux=max(d[n-1], aux);
    d[4]=v[3]+v[4];
    for (i=5;i<=n-2;i++)
        d[i]=max(d[i-1],d[i-3]+v[i-1]+v[i]);
    aux=max(d[n-2]+v[1]+v[n],aux);
    cout<<aux;
}