#include <iostream>
#include <vector>
#include <cmath>
 
using namespace std;
 
#define FOR(i,a,b) for(int i=a; i<=b; i++)
#define DOWN(i,a,b) for(int i=a; i>=b; i--)
 
typedef long long LL;
 
 
 
int main()
{
	int n;
	LL MAX = -9999999999;
 
	vector<LL> a,t3,T1,T2,T1MAX;
 
	cin>>n;	
 
 
	a.resize(n);
	FOR(i,0,n-1)
		cin>>a[i];
 
	t3.resize(n);
	FOR(i,2,n-1)
		t3[i] = a[i] + a[i-1] + a[i-2];
 
	T1.resize(n);
	T1[2] = t3[2];
	FOR(i,3,n-1)
		T1[i] = max(t3[i], T1[i-3] + t3[i]);	
 
	T2.resize(n);
	T2[n-3] = t3[n-1];// = a[n-3] + a[n-2] + a[n-1];
	DOWN(i,n-4,0)
		T2[i] = max(t3[i+2], T2[i+3] + t3[i+2]);
 
	T1MAX.resize(n);
	T1MAX[2] = T1[2];
	FOR(i,3,n-1)
		T1MAX[i] = max(T1MAX[i-1],T1[i]);
 
	FOR(j,3,n-3)
		MAX = max(MAX,T2[j] + T1MAX[j-1]);
 
	cout<<MAX<<endl;
 
	return 0;
}

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