#include <stdio.h>
#include <algorithm>

using namespace std;
FILE *f,*g;
int i,n,c[100004],a[100004],max1;
void calc (int start,int fin)
{   c[start+1]=a[start]+a[start+1];
    for (i=start+2;i<=fin;i++)
    {
        c[i]=0;
        c[i]=max (c[i-3]+a[i]+a[i-1],c[i-1]);
    }
}
int main()
{f=fopen ("oo.in","r");
 g=fopen ("oo.out","w");
 fscanf (f,"%d",&n);
 for (i=1;i<=n;i++)
      fscanf (f,"%d",&a[i]);
calc (3,n-2);
if (c[n-2]+a[1]+a[n]>max1) max1=c[n-2]+a[1]+a[n];
calc (1,n-1);
if (c[n-1]>max1) max1=c[n-1];
c[n]=c[n-1]=0;
c[n-1]=a[n]+a[n-1];
for (i=n-2;i>=2;i--)
    {
        c[i]=0;
        c[i]=max (c[i+3]+a[i]+a[i+1],c[i+1]);
    }

if (c[2]>max1) max1=c[2];
fprintf (g,"%d",max1);
    return 0;
}