#include<cstdio>
#include<algorithm>
using namespace std;
int n,a[100005],M[100005],N[100005],P[100005];
int main()
{
    int i;
    freopen("oo.in","r",stdin);
    freopen("oo.out","w",stdout);
    scanf("%d",&n);
    for (i=1;i<=n;++i)
        scanf("%d",&a[i]);
    M[2]=a[1]+a[2];
    N[3]=a[2]+a[3];
    P[1]=a[n]+a[1];
    for (i=4;i<=n;++i)
    {
        M[i]=max(a[i]+a[i-1]+M[i-3],M[i-1]);
        N[i]=max(a[i]+a[i-1]+N[i-3],N[i-1]);
        P[i]=max(a[i]+a[i-1]+P[i-3],P[i-1]);
    }
    printf("%d\n",max(max(M[n-1],N[n]),P[n-2]));
    return 0;
}