#include<stdio.h>
#include<mem.h>
unsigned int n,o[10001],nr[10001];
FILE* f=fopen("oo.in","r");
FILE* g=fopen("oo.out","w");

int main()
{fscanf(f,"%ld",&n);
int i,j;
unsigned long max,mx;
for(i=1;i<=n;i++) fscanf(f,"%d",&o[i]);

//aduna din primele 2 sectoare
nr[2]=o[1]+o[2];
nr[3]=nr[4]=nr[2];
max=nr[2];
for(i=5;i<=n-1;i++)
	{
	 if(nr[i-1]<nr[i-3]+o[i-1]+o[i])
			 nr[i]=o[i-1]+o[i]+nr[i-3];
	 else nr[i]=nr[i-1];
	 if(nr[i]>max) max=nr[i];
	}

for(i=1;i<=n;i++) nr[i]=0;

//aduna din sectoarele 2 si 3

nr[3]=nr[4]=nr[5]=o[2]+o[3];
for(i=6;i<=n;i++)
	{
	 if(nr[i-1]<nr[i-3]+o[i-1]+o[i])
			 nr[i]=o[i-1]+o[i]+nr[i-3];
	 else nr[i]=nr[i-1];
	 if(nr[i]>max) max=nr[i];
	}

for(i=1;i<=n;i++) nr[i]=0;
//memset(nr,0,sizeof(nr));

//aduna din sectoarele 1 si n

nr[1]=nr[2]=nr[3]=o[1]+o[n];
for(i=4;i<=n-2;i++)
	{
	 if(nr[i-1]<nr[i-3]+o[i-1]+o[i])
			 nr[i]=o[i-1]+o[i]+nr[i-3];
	 else nr[i]=nr[i-1];
	 if(nr[i]>max) max=nr[i];
	}

fprintf(g,"%ld",max);
fclose(g);
return 0;
}