#include<stdio.h>  
 #include<string.h>  
 #define  NMAX 110000  
 long x[NMAX],y[NMAX],rez,z[NMAX],i,j,n,m,k,l,a,s;  
 long max(long a, long b)  
 {  
     if (a>b)  
         return a;  
     return b;  
 }  
 void solve()  
 {  
     y[1]=x[1]+x[2];  
     z[2]=x[1]+x[2];  
     y[2]=x[2]+x[3];  
     y[2]=max(y[2],y[1]);  
   
     for (i=3;i<n;i++)  
     {  
         if (i!=n-1)  
         y[i]=max(z[i-2],y[i-3])+x[i]+x[i+1];  
         y[i]=max(y[i],y[i-1]);  
         z[i]=max(z[i-3],y[i-4])+x[i-1]+x[i];  
         z[i]=max(z[i],z[i-1]);  
   
         rez=max(rez,z[i]);  
         rez=max(rez,y[i]);  
     }  
     memset(y,0,sizeof(y));  
     memset(z,0,sizeof(z));  
   
 }  
 void mut()  
 {  
     a=x[n];  
     for (i=n;i>=2;i--)  
         x[i]=x[i-1];  
     x[1]=a;  
 }  
   
 int main()  
 {  
     freopen("oo.in","r",stdin);  
     freopen("oo.out","w",stdout);  
     scanf("%ld",&n);  
     for (i=1;i<=n;i++)  
         scanf("%ld",&x[i]);  
     solve();  
     mut();  
     solve();  
     mut();  
     solve();  

     printf("%ld\n",rez);  
   
     return 0;  
}