#include <iostream>
#include <cmath>
#include <vector>
 
using namespace std;
 
#define FOR(i,a,b) for(int i=a; i<b; i++)
#define REP(i,a,b) for(int i=a; i<=b; i++)
#define LL long long
 
 
int main()
{
	int n;
	vector<LL> a,t3,T;
	LL MAX = -999999999;
 
	cin>>n;
 
	a.resize(n+1);
	t3.resize(n+1);
	T.resize(n+1);
 
	REP(i,1,n)
		cin>>a[i];
 
	REP(i,3,n)
		t3[i] = a[i] + a[i-1] + a[i-2];
 
	REP(i,3,n)
	{
		T[i] = max(t3[i],t3[i] + T[i-3]);
		MAX = max(T[i],MAX);
	}	
 
	cout<<MAX<<endl;
 
	return 0;
}

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