#include<stdio.h>
int n,i,s[100001],v[100001],smax1,smax2,poz;
FILE *in=fopen("oo.in","rt"),*out=fopen("oo.out","wt");
int main()
{
	fscanf(in,"%d",&n);
	for(i=1;i<=n;i++)
	{
		fscanf(in,"%d",&v[i]);
		if(i>1&&i<=n)
			s[i]=v[i]+v[i-1];
		if(i==n)
			s[1]=v[i]+v[1];
			
	}
	for(;;)
	{
		smax1=0;
		for(i=1;i<=n;i++)
		 if(i!=n)
			{
			if(smax1<=s[i]&&s[i]!=-1&&s[i-1]!=-1&&s[i+1]!=-1)
			 {
				smax1=s[i];
				poz=i;
			 }
      }
			else
			 if(smax1<=s[i]&&s[i]!=-1&&s[i-1]!=-1&&s[1]!=-1)
				{
				 smax1=s[i];
         poz=i;
				}
		smax2+=smax1;
		if(poz!=n)
		{
		s[poz]=-1;
		s[poz-1]=-1;
		s[poz+1]=-1;
		}
		else
		{
		s[poz]=-1;
		s[n-1]=-1;
    s[1]=-1;
		}
		if(smax1==0)
			break;
	}
	fprintf(out,"%d",smax2);
	
	return 0;
}