#include<stdio.h>
#include<string.h>
int n;
long v[10010],max;

long maxim(long a, long b)
{
	if(a<b)
		a=b;
	return a;
}

void rez(int x)
{
	long s[10010];
	memset(s,0,sizeof(s));
	int i;
	for(i=2+x;i<n+x;i++)
		s[i]=maxim(s[i-1],s[i-3]+v[i]+v[i-1]);
	max=maxim(max,s[n+x-1]);
}

void read()
{
	freopen("oo.in","r",stdin);
	freopen("oo.out","w",stdout);
	int i;
	scanf("%d",&n);
	for(i=4;i<=n+3;i++)
		scanf("%ld",&v[i]);
	v[1]=v[n+1];
	v[2]=v[n+2];
	v[3]=v[n+3];
	rez(1);rez(2);rez(3);
	printf("%ld\n",max);
}

int main()
{
	read();
	return 0;
}