#include <iostream>
#include <cmath>
#include <vector>
 
using namespace std;
 
#define FOR(i,a,b) for(int i=a; i<b; i++)
#define LL long long
 
 
int main()
{
	int n;
	vector<LL> T;
	LL a;
 
	cin>>n;
	T.resize(n+1);
 
	FOR(i,1,n+1)
	{
		cin>>a;
		T[i] = T[i-1] + a;
	}
 
	LL MAX = -9999999999;
 
	FOR(i,1,n+1)
	{
		FOR(j,i,n+1)
		{
			if((j-i+1)%3 == 0)
			{
				LL t = T[j] - T[i-1];
				MAX = max(t,MAX);
			}
		}
	}
 
	cout<<MAX<<endl;
 
	return 0;
}

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