Giới thiệu
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;
}