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

#define NDEBUG
#include <cassert>


typedef long long ll;
typedef long double Double;
typedef unsigned long long ull;
typedef pair<int,int> ii;
typedef pair<ll,ll> llll;
typedef pair<double,double> dd;

typedef vector<int> vi;
typedef vector<vector<int>> vvi;
typedef vector<ii> vii;
typedef vector<vector<ii>> vvii;
typedef vector<ll> vll;
typedef vector<string> vs;
typedef vector<double> vd;
typedef vector<long double> vD;

#define sz(a)  int((a).size())
#define pb  push_back
#define eb  emplace_back
#define FOR(var,from,to) for(int var=(from);var<=(to);++var)
#define rep(var,n)  for(int var=0;var<(n);++var)
#define rep1(var,n)  for(int var=1;var<=(n);++var)
#define repC2(vari,varj,n)  for(int vari=0;vari<(n)-1;++vari)for(int varj=vari+1;varj<(n);++varj)
#define ALL(c)  (c).begin(),(c).end()
#define RALL(c)  (c).rbegin(),(c).rend()
#define tr(i,c)  for(auto i=(c).begin(); i!=(c).end(); ++i)
#define found(s,e)  ((s).find(e)!=(s).end())
#define mset(arr,val)  memset(arr,val,sizeof(arr))
#define mid(x,y) ((x)+((y)-(x))/2)
#define IN(x,a,b) ((a)<=(x)&&(x)<=(b))
#define cons make_pair

#define PQ(T) priority_queue<T>
#define RPQ(T) priority_queue<T,vector<T>,greater<T>>

template<class T> inline void amin(T & a, T const & b) { a = min(a, b); }
template<class T> inline void amax(T & a, T const & b) { a = max(a, b); }

inline ll square(ll x) { return x * x; }
inline ll gcd(ll a, ll b) { while(a) swap(a, b%=a); return b; }
template <typename T>
inline T mod(T a, T b) { return ((a % b) + b) % b; }


const ll MOD=1000000007LL;

ll ADD(ll x, ll y) { return (x+y) % MOD; }
ll SUB(ll x, ll y) { return (x-y+MOD) % MOD; }
ll MUL(ll x, ll y) { return x*y % MOD; }
ll POW(ll x, ll e) { ll v=1; for(; e; x=MUL(x,x), e>>=1) if (e&1) v = MUL(v,x); return v; }
ll DIV(ll x, ll y) { /*assert(y%MOD!=0);*/ return MUL(x, POW(y, MOD-2)); }

#define INTSPACE 12
char _buf[INTSPACE*1000000 + 3];

int loadint() {
    if (fgets(_buf, INTSPACE+3, stdin)==NULL) return 0;
    return atoi(_buf);
}

int loadvec(vector<int>& v, int N=-1) {
    if (N == 0) {
        v.clear();
        return 0;
    }
    if (N == -1) {
        N = loadint();
        if (N==0) return 0;
    }
    int bufsize = INTSPACE*N + 3;
    if (fgets(_buf, bufsize, stdin)==NULL) return 0;
    v.resize(N);

    int i=0;
    bool last = false;
    for (char *p=&_buf[0]; ;) {
        char *q = p;
        while (*q > ' ') ++q;
        if (*q == 0x0D || *q == 0x0A) last = true;
        *q = 0;
        v[i++] = atoi(p);
        if (last || i == N) break;
        p = q+1;
    }
    return i;
}
void read_cr() {
    fgets(_buf, 256, stdin);
}




/*
template <typename T>
vector<T> divisors(T x){
    vector<T> res;
    T sq = sqrt(x);
    for (int n=1; n<=sq; ++n){
        T q = x / n, r = x % n;
        if (r) continue;
        res.push_back(n);
        if (q != n) res.push_back(q);
    }
    return move(res);
}
*/

template <typename T>
vector<T> divisors(T x){
    deque<T> dq;
    T s = sqrt(x);
    if (x % s == 0) {
        dq.push_front(s);
        T t = x / s;
        if (t > s) dq.push_back(t);
    }
    for (T n=s-1; n>=1; --n) {
        if (x % n == 0) {
            dq.push_front(n);
            dq.push_back(x / n);
        }
    }
    return vector<T>(dq.begin(), dq.end());
}


struct P {
    int cnt;
    ll vsum;
    ll vmax;
    bool stopped;
};
inline ostream& operator<<(ostream &s, P v)
{
    return s << "{ " << v.cnt << ", " << v.vsum << ", " << v.vmax << " }";
}

ll solve(int N, vi& s) {
    int W = N-1;
    int dmax = (W-1)/2;
    vector<P> lu(dmax+1, P {0,0,LLONG_MIN,false});

    ll ans = 0;
    for (int x=1; x<W; ++x) {
        vi di = divisors(x);
        ll sum = s[x] + s[N-1-x];
        for (int d: di){
            if (d > dmax) break;
            if (x == W-x) {
                lu[d].stopped = true;
                continue;
            }
            if (lu[d].stopped) continue;

            int cnt = lu[d].cnt + 1;
            bool dy = (W % d == 0);
            if (dy && d*cnt > dmax) {
                continue;
            }
            if (W-d*cnt < d) {
                continue;
            }
            lu[d].cnt++;
            lu[d].vsum += sum;
            amax(lu[d].vmax, lu[d].vsum);
            amax(ans, lu[d].vmax);
        }
    }
    return ans;
}

int main() {
    vi s;
    int N = loadvec(s);
    cout << solve(N,s) << endl;
    return 0;
}


Measured memory_bytes: 3200