#include<stdio.h>
#define dim 100010

int i,n,max,V[dim],D[dim];

FILE*f=fopen("oo.in","r");
FILE*g=fopen("oo.out","w");

int maxim(int a,int b){
	if(a>b)
		return a;
	return b;
}

int main(){
	
	fscanf(f,"%d",&n);
	for(i=1;i<=n;i++)
		fscanf(f,"%d",&V[i]);
	
	D[1]=D[2]=D[3]=D[n]=V[1]+V[2];
	max=D[1];
	for(i=4;i<=n-3;i++){
		D[i]=maxim(D[i-1],V[i]+V[i+1]+D[i-4]);
		if(D[i]>max)
			max=D[i];
	}
	D[1]=D[2]=D[n]=D[n-1]=V[1]+V[n];
	for(i=3;i<=n-4;i++){
		if(i==3)
			D[i]=maxim(D[i-1],V[i]+V[i+1]);
		else
			D[i]=maxim(D[i-1],V[i]+V[i+1]+D[i-4]);
		if(D[i]>max)
			max=D[i];
	}
	D[1]=D[n]=D[n-1]=D[n-2]=V[n]+V[n-1];
	for(i=2;i<=n-5;i++){
		if(i<4)
			D[i]=maxim(D[i-1],V[i]+V[i+1]);
		else
			D[i]=maxim(D[i-1],V[i]+V[i+1]+D[i-4]);
		if(D[i]>max)
			max=D[i];
	}
	if(n==3)
		max=maxim(V[1]+V[2],V[2]+V[3]);
	if(n==2)
		max=V[1]+V[2];
	fprintf(g,"%d",max);
	return 0;
}