#include<cstdio>
#include<algorithm>
#include<cstring>
#define Nmax 100000
using namespace std;
int n,i,j,p,q,nr,a[Nmax],v[Nmax];
int sol;
int main()
{
    freopen("oo.in","r",stdin);
    freopen("oo.out","w",stdout);
    scanf("%d",&n);
    for (i=1;i<=n;i++)
    scanf("%d",&v[i]);
    v[n+1]=v[1];
    a[2]=v[1]+v[2];
    for (i=3;i<n;i++)
    a[i]=max(a[i-1],a[i-3]+v[i]+v[i-1]);
    sol=max(sol,a[n-1]);
    a[1]=a[2]=0;
    for (i=3;i<=n;i++)
    a[i]=max(a[i-1],a[i-3]+v[i]+v[i-1]);
    sol=max(sol,a[n]);
    a[1]=a[2]=a[3]=0;
    for (i=4;i<=n+1;i++)
    a[i]=max(a[i-1],a[i-3]+v[i]+v[i-1]);
    sol=max(sol,a[n+1]);
    printf("%d",sol);
    return 0;
}