#include <fstream>
std::ifstream f1("oo.in");
std::ofstream f2("oo.out");

int main()
{
	long n, a, b, t, s=0, s0=0, s1=0, s2=0, i;
	f1>>n;
	f1>>a;
	t=a;
	for (i=0; i<(n-1); i++)
	{
		f1>>b;
		if ((i%3)==0)
			s0+=a+b;
		if ((i%3)==1)
			s1+=a+b;
		if ((i%3)==2)
			s2+=a+b;		
		a=b;
	}//for i
	b=t;
	if ((i%3)==0)
		s0+=a+b;
	if ((i%3)==1)
		s1+=a+b;
  if ((i%3)==2)
		s2+=a+b;		
	s=s0;
	if (s1>s)
		s=s1;
	if (s2>s)
		s=s2;
	f2<<s;
	f1.close();
	f2.close();
	return 0;
}//main