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

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

//aduna din primele 2 sectoare
nr[2]=o[1]+o[2];
max=nr[2];
for(i=3;i<=n-1;i++)//din ultimul sector nu mai aduna
	{
	 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]=o[2]+o[3];
for(i=4;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;

//aduna din sectoarele 1 si n

nr[1]=nr[2]=o[1]+o[n];
for(i=3;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,"%lu\n",max);
fclose(g);
return 0;
}