#include<fstream>
using namespace std;
int v[10000],i,n,D[100000],x;
int maxim(int x,int y)
	{
		if(x>y) return x;
		else return y;
}

int main()
{
	ifstream f("oo.in");
	ofstream g("oo.out");
	f>>n;
	for(i=1;i<=n;i++)
		f>>v[i];
	D[1]=0;
	D[2]=0;
	D[3]=v[2]+v[3];
	for(i=4;i<=n;i++)
		D[i]=maxim(D[i-1],v[i]+v[i-1]+D[i-3]);
	x=D[n];
	D[1]=0;
	D[2]=v[1]+v[2];
	D[3]=v[1]+v[2];
	for(i=4;i<=n-1;i++)
		D[i]=maxim(D[i-1],v[i]+v[i-1]+D[i-3]);
	x=maxim(x,D[n-1]);
	v[n+1]=v[1];
	for(i=2;i<=n+1;i++)
		v[i-1]=v[i];
	D[1]=0;
	D[2]=0;
	D[3]=v[2]+v[3];
	for(i=4;i<=n;i++)
		D[i]=maxim(D[i-1],v[i]+v[i-1]+D[i-3]);
	x=maxim(x,D[n]);
	g<<x;
	return 0;
}