#include <bits/stdc++.h>
using namespace std;
int b[100005];
map<int, int> d;
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n;
  cin >> n;
  for (int i = 1; i <= (n + 1) / 2; i++) b[i] = i;
  for (int i = (n + 1) / 2 + 1; i <= n; i++) b[i] = b[n - i + 1];
  for (int i = 1; i <= n; i++) {
    int x;
    cin >> x;
    if (i <= (n + 1) / 2)
      d[b[i] - x]++;
    else
      d[b[i] - x]++;
  }
  int res = n;
  for (auto &x : d) {
    if (x.first > 0) continue;
    res = min(res, n - x.second);
  }
  cout << res;
}
