#include <bits/stdc++.h>
using namespace std;
using LL = long long;

template<typename T>bool chmax(T&a,T b){if(a<b){a=b;return true;}return false;}
template<typename T>bool chmin(T&a,T b){if(a>b){a=b;return true;}return false;}


// std::vector Declaration
template<typename T>
vector<T> make_v(size_t a) { return vector<T>(a); }
template<typename T,typename... Ts>
auto make_v(size_t a,Ts... ts) {
   return vector<decltype(make_v<T>(ts...))>(a,make_v<T>(ts...));
}

// std::vector Initialization
template<typename T>
void fill_all(T& arr, const T& v) { arr = v; }
template<typename T, typename U>
void fill_all(T& arr, const U& v) { for (auto& i : arr) fill_all(i, v); }

// std::vector Debug
template<typename T>
ostream& operator<<(ostream& os, const vector<T>& v) {
   os << "[";
   bool a = 1;
   for (auto e : v ) {
      os << (a ? "" : " "); 
      os << e;
      a = 0;
   }
   os << "]";
   return os;
}

// std::pair Debug
template<typename T, typename U>
ostream& operator<<(ostream& os, const pair<T, U>& p) {
   os << "(" << p.first << " " << p.second << ")";
   return os;
}

// std::set Debug
template<typename T>
ostream& operator<<(ostream& os, const set<T>& st) {
   os << "{";
   bool a = 1;
   for (auto e : st) {
      os << (a ? "" : " ");
      os << e;
      a = 0;
   }
   os << "}";
   return os;
}

// std::multiset Debug
template<typename T>
ostream& operator<<(ostream& os, const multiset<T>& st) {
   os << "{";
   bool a = 1;
   for (auto e : st) {
      os << (a ? "" : " ");
      os << e;
      a = 0;
   }
   os << "}";
   return os;
}

// std::map Debug
template<typename T, typename U>
ostream& operator<<(ostream& os, const map<T, U>& mp) {
   os << "{";
   bool a = 1;
   for (auto e : mp) {
      os << (a ? "" : " ");
      os << e.first << ":" << e.second;
      a = 0;
   }
   os << "}";
   return os;
}

// std::tuple Debug
template<int N,class Tuple>
void out(ostream &os,const Tuple &t){}
template<int N,class Tuple,class H,class ...Ts>
void out(ostream &os,const Tuple &t){
   if(N)os<<" ";
   os<<get<N>(t);
   out<N+1,Tuple,Ts...>(os,t);
}
template<class ...Ts>
ostream& operator<<(ostream &os, const tuple<Ts...> &t){
   os<<"(";
   out<0,tuple<Ts...>,Ts...>(os,t);
   os<<")";
   return os;
}

// Debug
#define DUMP(x) cout<<#x<<" = "<<(x)<<endl

// trio (first, second, third)
template<typename T, typename U, typename V>
struct trio {
   T first;
   U second;
   V third;

   bool operator<(const trio<T,U,V>& rhs) const {
      pair<T,pair<U,V>> l{first,{second,third}},
         r{rhs.first,{rhs.second,rhs.third}};
      return l < r;
   }

   bool operator>(const trio<T,U,V>& rhs) const {
      return rhs < *this;
   }
};

// trio Debug
template<typename T, typename U, typename V>
ostream& operator<<(ostream& os, const trio<T, U, V>& t) {
   os << "(" << t.first << " " << t.second << " " << t.third << ")";
   return os;
}

struct edge { int to, cost; };

const LL LINF = 1LL<<60;
const int IINF = 1<<30;
const LL MOD = 1e9+7;

int main()
{
   int N; cin >> N;
   vector<LL> s(N);
   for (int i = 0; i < N; ++i) {
      cin >> s[i];
   }

   LL ans = 0;
   for (int d = 1; d < N; ++d)
   {
      if ((N-1) % d == 0)
      {
         LL sum = 0;
         for (int i = 1; d*i < N-1-d*i; ++i) {
            sum += s[d*i] + s[N-1-d*i];
            chmax(ans, sum);
         }
      }
      else
      {
         LL sum = 0;
         for (int i = 1; d*(i+1) < N; ++i) {
            sum += s[d*i] + s[N-1-d*i];
            chmax(ans, sum);
         }
      }
   }

   cout << ans << endl;

   return 0;
}


Measured memory_bytes: 1024