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

#ifdef DEBUG
auto &operator<<(auto &o, pair<auto, auto> p) {
    return o << "(" << p.first << ", " << p.second <<")";
}
auto operator<<(auto &o, auto x)-> decltype(x.end(), o) {
    o << "{";int i = 0;
    for(auto e : x) o << ", "+!i++<<e;
    return o <<"}";
}
#define debug(x...) cerr << "["#x"]: ",[](auto...$){((cerr<<$<<"; "),...)<<endl;}(x)
#else
#define debug(...) {}
#endif

#define all(x) x.begin(), x.end()
#define sz(x) (int)(x).size()
#define pb push_back
#define fi first
#define se second
typedef pair <int, int> pii;


constexpr int N = 1e5+7;
int elem[N];
int rem[N];
uint8_t pot[N];
uint8_t ok[N];
uint8_t comp[N];

bool okjmp(int const n, int const jmp) {
    debug("CHECKING ", n, jmp);
    int cur = 0;

    for (int i=0; i<jmp; ++i) {
        rem[i] = 0;
    }

    int j = 0;
    for (int i=0; i<=n-jmp; ++i) {
        cur -= rem[j];
        int const here = elem[i] - cur;
        
        if (here < 0) {
            debug(here, i, cur, elem[i]);
            return false;
        }

        cur += here;
        rem[j] = here;
        j++;
        if (j >= jmp) j-=jmp;
    }

    j = (n - jmp + 1) % jmp;

    for (int i=n-jmp+1; i<n; ++i) {
        cur -= rem[j];
    
        if (cur != elem[i]) {
            debug(i, cur, elem[i]);
            return 0;
        }
        j++;
        if (j >= jmp) j-=jmp;
    }
    return true;
}


void test() {
    debug("TC______________________");
    int n; cin>>n;

    for (int i=0; i<n; ++i) {
        cin>>elem[i];
        pot[i+1] = 1;

    }
    
    int chd = 0;
    for (int i=2; i<=n; ++i) {
        if (!comp[i]) {
            bool chk = okjmp(n, i);
            chd++;
            ok[i] = pot[i] = chk;
            debug(i, chk);

            for (int j=i; j<=n; j+=i) {
                comp[j] = 1;
                pot[j] &= chk;
            }
        }
    }
    
    int res = 1; 

    for (int i=n; i>=res; --i) {
        if (ok[i]) {
            res = i;
            break;
        }
        if (pot[i]) {
            bool chk = okjmp(n, i);
            chd++;
            if (chk) {
                res = i;
                break;
            }
        }
    }

    debug(chd);
    cout<<res<<'\n';

}

signed main() {
  ios_base::sync_with_stdio(0); cin.tie(0);
  int t = 1; 
  while (t--) {
    test();
  }
}