#include<stdio.h>
FILE*f=fopen("oo.in","r");
FILE*g=fopen("oo.out","w");
long sol,oo[122206],a[122206],n,s1,s2,s3;
long max(long a, long b)
  {
  if(a>b) return a;
  else return b;
  }
int main()
  {
  fscanf(f,"%ld",&n);
  long i;
  for(i=1;i<=n;++i) fscanf(f,"%ld",&oo[i]);
  if(n>2)

   {

  a[2]=oo[1]+oo[2];
  
  for(i=3;i<=n;++i) a[i]=max(oo[i]+oo[i-1]+a[i-3],a[i-1]);

  s1=a[n-1];

  for(i=0;i<=n;++i) a[i]=0;

  for(i=3;i<=n;++i)

     a[i]=max(oo[i]+oo[i-1]+a[i-3],a[i-1]);

  s2=a[n];

  for(i=0;i<=n;++i) a[i]=0;

  a[1]=a[2]=oo[1]+oo[n];

  for(i=3;i<n-1;++i) a[i]=max(oo[i]+oo[i-1]+a[i-3],a[i-1]);

  s3=a[n-2];

   }

  else
    {
    s1=oo[1]+oo[0],s2=s1,s3=s1;
    }

  sol=max(max(s1,s2),s3);

  fprintf(g,"%ld\n",sol);

  return 0;
  }